AITA for Discovering My Best Friend Secretly Dating My Ex-Girlfriend for Months?

A 28-year-old guy thought his best friend, Alex, was the one person he could always count on. Then he found out Alex had been quietly dating his ex, Sarah, for months, including a full stretch where Alex sat there, friendly and supposedly honest, while OP was still processing the breakup.

OP and Sarah split amicably over a year ago, but Alex knew the history. Even so, Alex kept the relationship secret and then lied again when OP confronted him ten months into the affair. The excuse was basically, “We didn’t want to hurt your feelings,” which might sound gentle until you realize it also means they chose deception over trust.

Now OP is stuck wondering if he misread the whole friendship, and whether loyalty even exists when it comes to your ex.

Original Post

I (28M) have been best friends with Alex (29M) since college. We've always had each other's backs, or so I thought.

Until I found out that Alex had been secretly dating my ex-girlfriend, Sarah, for the past few months. Sarah and I split amicably over a year ago due to mutual differences.

Since our breakup, Alex and I discussed past relationships, and he knew Sarah and I had history. Yet, he not only kept this budding relationship from me but also lied when I confronted him ten months into their secret affair.

They justified it by claiming they didn't want to hurt my feelings, but I couldn't believe they deceived me for so long. I feel utterly betrayed by my best friend and ex-girlfriend, unsure of how to handle this situation.

So AITA?

The Betrayal Cuts Deep

This situation isn’t just about OP losing out on a romantic relationship; it’s about the profound sense of betrayal from someone he considered his best friend. Discovering that Alex has been secretly dating Sarah for months not only blindsides OP but raises uncomfortable questions about loyalty. How could Alex, someone OP likely confided in during his breakup, choose to pursue a relationship with his ex without any heads-up?

The emotional fallout here is palpable. OP’s feelings of confusion and anger are entirely justified, and it creates a tension many can relate to. Friendships have unwritten rules, and crossing those lines can lead to long-lasting rifts. For OP, this revelation might mean reassessing who he can truly trust moving forward.

OP didn’t just discover a secret relationship, he discovered it after Alex and Sarah’s months of “we’re totally fine” energy.

Comment from u/techie_guy123

NTA. That's a major breach of trust, especially from your best friend. They should've been honest from the beginning.

Comment from u/theatre_fanatic

YTA. Once you break up, the past is the past. Your friend might really care about Sarah, and it's their choice who they date.

Comment from u/pizza_lover212

Dang, that's tough, OP. NTA. Your friend should've at least been upfront about it. This must be really hurtful.

Comment from u/animal_whisperer

Ugh, this sucks. NTA. It's one thing to date an ex, but keeping it a secret is a whole new level of betrayal.

The tricky part is that Alex and OP discussed past relationships after the breakup, so this wasn’t some random new connection.

Comment from u/fashionista87_

That's a messy situation. NTA, though. Your friend crossed a line by hiding it and lying about it. Sorry you're dealing with this.

It’s also like the best friend who lied about a secret gift exchange.

Comment from u/music_junkie56

Oof, this is a tough one. NTA. Honesty is key, especially among friends. Sounds like a tough conversation ahead.

Comment from u/bookworm_gal

I can't even imagine, OP. NTA. Your friend should've been open about this from the start. Time for some serious conversations.

That’s when the lie hits harder, because OP confronted Alex ten months in and Alex still chose the cover story.

Comment from u/coffeeholic89

NTA. It's a shady move on both their parts. Your feelings are valid, and you have every right to be upset about this.

Comment from u/theatre_geek21

Hmm, that's a tough spot. NTA, though. Your friend should've been transparent. It's hard when trust is broken like that.

Comment from u/running_addict

Oh man, that's a rough situation to be in. NTA. Your friend should've been more upfront, especially given your history with Sarah.

Meanwhile, the comments are split, with one camp calling it a major betrayal and the other saying Sarah is “the past,” not the problem.

We'd love to hear your take on this situation. Share your thoughts below.

This story resonates deeply because it highlights the often-blurry lines between friendship and romantic relationships. Many readers have likely found themselves in similar situations, where romantic interests overlap with close friendships. The fact that Alex didn’t disclose his relationship with Sarah complicates things further. Was he waiting for the right moment, or did he know he was stepping into dangerous territory?

What makes this even more complicated is how relationships often evolve. It’s common for friends to date exes, but secrecy can breed resentment. The Reddit community is divided, with some siding with OP, arguing that Alex’s actions were a blatant betrayal, while others might see it as an inevitable consequence of moving on. This moral gray area keeps the debate alive.

This scenario is a vivid reminder of how intertwined relationships can become messy and complicated. OP’s sense of betrayal from both Alex and Sarah reflects a larger issue that many can relate to: the expectations we hold for our friends. As readers, we’re left wondering how OP should navigate this painful revelation. Can trust be rebuilt, or is it time to cut ties for good? What would you do in OP’s shoes?

In this situation, OP's feelings of betrayal are understandable given the long-standing friendship with Alex and the secretive nature of his relationship with Sarah. Despite having ended things with Sarah amicably, the fact that Alex chose to hide their budding romance for months raises significant questions about loyalty and honesty. This scenario illustrates how easily trust can be eroded when friends cross emotional boundaries.

He might have lost Sarah and Alex at the same time, and now he’s questioning what “best friend” even means.

Want the “don’t support dating my cheating ex” boundary breakdown? Read this AITA where a friend dates a cheating ex.