AITA for telling my sister she lost me the second she even considered dating my ex who gave me an STD and didn’t tell me?

In the wake of a shattered trust and lingering betrayal, emotions can run hotter than blood. The unfolding drama of a sister’s decision to date a man who once caused severe emotional and physical harm sets the stage for a raw and honest confrontation. Here, every word is loaded with decades of unresolved pain and the stark reality that some bridges, once burned, cannot be easily rebuilt.

Against a backdrop of family memories that once promised unconditional love, this story exposes how past wounds can dictate present relationships. The decision to draw an unyielding line—declaring that loyalty and safety come before familial bonds—resonates as a powerful reminder of personal boundaries. With a mix of regret, defiance, and the need for self-protection, the narrative invites readers to reconsider where forgiveness ends and self-respect begins.

‘AITA for telling my sister she lost me the second she even considered dating my ex who gave me an STD and didn’t tell me?’

I (28f) was with a guy called Jason (29m) when we were 20/21 years old. We broke up when I was 22 after I'd found out he had not only cheated on me, but knew he contracted an STD from sleeping around and didn't tell me. He had known about it and he was told he needed to speak to any s**ual partners because of the risks associated with this STD to fertility and he said nothing.

I remember when I told my family what had happened they were all there to support me and my sister (27f) was one of them. I did move on and I met my husband a year after breaking up with Jason. And thankfully I was able to get pregnant and we have a baby together. But I never forgot about the fact Jason did what he did.

Cheating was bad enough but you can move on. The STD was where it became not only unforgivable but I would have taken issue with anyone in my family even becoming friends with him after that point. But then three months ago my sister asked me if I would be okay with her dating Jason.

She told me she didn't want to lose me but they had met again after several years and she liked him and he'd changed. I walked away from my sister without saying a word and she started dating Jason officially. Though when she came to me like she did and asked me like she did, I would guess they had been unofficial before that point and not just friendly.

I have shut my sister out of my life and she has not been allowed to come and meet my child. The rest of the family stands me and what I decided but they have not shut her out of their lives. Which is totally fine and not an issue for me. But my sister doesn't like that and she has tried to get in touch with me several times and has cried and asked me to hear her out and to talk to her.

The fact I have run into her once since and I ignored her. She was talking to me but I acted like she was a ghost I couldn't see or hear. So she ambushed me at my house the other day and told me she doesn't want to lose me and she'll break up with Jason if I stop ignoring her and we can go back to being sisters.

I told her she lost me the second she even considered dating him. I told her I might not have known about it in that moment but once I heard she wanted to date him, knowing what he did to me, it was over. She's crying about it now and our family are refusing to hear her cries about it.

My baby sister (24) told me she's trying to get the rest of the family to confront me about it but nobody will. She does think our sister is genuinely hurt about this but she feels like it's her own fault. And I agree. But I know what I said to her might still be overly harsh because even thinking about it without acting on it would have led to this, which might be wrong of me. So I'm here to ask AITA?

The complexities of intimate betrayal often extend far beyond the direct relationship, permeating even the ties we share with family. When trust is shattered—not only through infidelity but compounded by deceit regarding health and safety—it’s natural for strong emotional reactions to surface. The decision to cut ties reflects a hard-earned boundary against re-experiencing such trauma.

Experts in relationship dynamics note that the repercussions of betrayal are multifaceted. The hurt inflicted by undisclosed risks, like contracting an STD, often disrupts not only personal confidence but also the entire support system built over years. In settings where trust is foundational, even the mere consideration of aligning with a person who once caused harm can feel like a profound betrayal. This reaction isn’t just about romantic interest but about preserving the integrity of one’s emotional well-being.

According to Dr. Laura Markham, a respected clinical psychologist and parenting expert, “When our personal boundaries are violated, the pain transcends the immediate situation and alters how we approach trust in all relationships.” Her insight emphasizes that while forgiveness is a personal journey, it should never come at the cost of one’s well-being. For some, maintaining self-respect means accepting that some actions cannot be overlooked, no matter the passage of time.

The expert further advises that communication, however painful, is crucial to understanding the root causes behind such decisions. Establishing clear personal values and recognizing that every relationship has its own non-negotiable limits is essential. In this context, the sister’s decision reopens old wounds, and the ensuing fallout serves as a cautionary tale: choosing to engage with a past fraught with betrayal can have irreversible consequences. Ultimately, protecting oneself sometimes means accepting the loss of a familial bond, as difficult as it may be, to ensure emotional safety and long-term healing.

Here’s how people reacted to the post:

Here are some candid responses from the Reddit community—raw, unfiltered, and biting in their honesty. The commenters broadly agree that the betrayal involved isn’t something to overlook lightly, and that choosing to date someone with such a painful past is a step too far. Their remarks range from outright support of the decision to harsh critiques of the sister’s judgment.

AdAccomplished6870 − People who are bad people, cheaters, abusers, etc, have a charming and likable side. That is how they get their victims or partners. I am always amused when someone says 'No, he's changed.' Has he? Or is he just showing you the side of him he wants you to see? If he has changed, can the sister articulate how he has changed and what drove him to change?

How has he made amends, or at least acknowledged the person he was? In 99.999999% of the 'He's changed' cases, he has not changed at all, he is just in the love bombing stage. The person who believes he has changed almost always finds out the hard way that he is still a cheater, still selfish, still dishonest.

Huge_Mistake_3139 − NTA - I’m not sure what your sister expected to happen, but that’s pretty low. I am curious how holidays and family gatherings work. Since your family still allows her to show up, do you just not go?

Pixiegirl_vonKorea − Why some sinsters always like the leftover of their sisters

SpiteWestern6739 − NTA, anyone wanna take bets on how long it takes for him to start cheating on the sister? And whether she'll be lucky and just catch chlamydia off him or if it will be something more permanent this time around?

serial-tea-fiend − NTA. I can’t fathom in a million years being with someone I know has slept with my sister. She must’ve liked him when you were with him.. Question: Is it possible that she was one of the APs at that time?

Buttered_Crumpet09 − NTA. Your sister seems to think that Jason is the issue and if she gets rid of him, it'll undo the damage. The thing is that he isn't the problem. She is. She deliberately chose to date your ex, which in and of itself is weird and wrong, but she didn't just choose any ex.

She decided to pick the guy who hurt you the most, who cheated and who willingly gave you an STD knowing it could cost you your chance at having children. All that is bad enough, but the fact that she crept about meeting him and began dating him without mentioning anything makes it worse.

She didn't speak to you about it before anything happened to see how you'd feel, she basically went,

The damage was done the moment she decided to get involved with him in any way. She made it clear that he and his wandering penis were more important than you, your feelings, and her relationship with you. I have to ask, what do you think she expected with this? Is she normally this thick-headed and oblivious?

Nervous-Craft-4613 − Of all the men in the world (and we're talking billions) your sister just had to date your ex. 

Awesomekidsmom − NTA. What she is learning is very simple -. the dildo of consequences doesn’t use lube! She made a conscious decision to be with a guy who maliciously infected you with a disease- it’s simply unforgivable

iknowsomethings2 − NTA. She FAFO, and you will not be there for her when he cheats on her. Sucks to suck.. I’m glad your family is standing by you and not letting her get away with this BS

CAgirl17 − NTA I’m honesty confused on why she thought you would be okay with this? Also, who even wants ti dare their siblings ex?! I’d never think to do that to my sister, nor would I want to.

In conclusion, this deeply personal narrative is not merely about a romantic decision gone awry; it’s about the irreversible impact of trust broken in the most intimate ways. The story challenges us to consider whether some betrayals are unforgivable and where the balance lies between familial love and self-preservation. What would you do when faced with a similar heart-wrenching dilemma? Join the conversation and share your thoughts—can the bonds of family ever mend after such a breach, or are some lines simply untraversable?

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