How do you handle an ex who won’t be fully honest about what they did to end the relationship?

I’m struggling with how to handle my ex after a breakup where honesty and disclosure have been a huge issue.

Here’s the short version: My ex told me out of nowhere during our vacations apart that she had lost feelings and wanted a “break.” I told her I don’t believe in breaks, so we broke up. Within days, she slept with someone else. When we later met to talk, it shifted into reconciliation. I was vulnerable and asked her directly if she had been with anyone. She said no. It wasn’t until after we had already slept together again that she admitted she had been with someone — but minimized it and claimed it didn’t “count” because we were broken up at the time.

The problem is the lack of full honesty. I’ve since pieced together that she planned this beforehand. I confronted her that her story doesn’t fully line up, but she keeps insisting it was only when we were apart, so she did nothing wrong. To me, the way she handled it was a severe breach of trust — planning while we were together, waiting until after we were intimate to disclose, and trickle-truthing instead of being upfront.

She continues to say I’m overreacting since “we weren’t together.” But to me, this wasn’t just about the act itself, but about honesty, timing, and respect. It feels like she wanted to keep me as a backup, hoping I’d accept the “break,” while she already had a plan and had someone lined up.

I know I’ll probably never get the full truth from her and that’s something I’m struggling with. It still eats at me that she won’t own her role in what actually caused the breakup — she just frames it as a harmless hookup that shouldn’t matter because we broke up.

My question is:
How have you handled an ex who refuses to be fully honest or in denial about the real reasons a breakup happened? Especially when the trickle-truth makes it harder to get closure?

I don’t want to keep going in circles or trying to extract honesty that will never come. I just want to know how others found peace when their ex wouldn’t take full accountability.