I'm extremely confused about something, and I need input.

hi. so, I've been thinking about something that happened during my relationship with my ex, and I'm extremely confused about it.

context : I came out to them about the fact that I'm asexual, and at some point, they just proposed to have an open relationship. I agreed. tho I have to admit that, when they told me about a hook up in messages, I wasn't feeling good, but I thought to myself that I was in the wrong for feeling sad ( never told them about how I felt ). we've gone further in our relationship, and they kept going to other people ( I said nothing, 'cause once again, I felt in the wrong for feeling awful about this ). then came the break up ( which was for other reasons ). 2 months after it, they already found a girlfriend and even moved out with her. I'm deeply confused about what all of this could mean about my ex.

I'm sorry if I didn't explained well, I sometimes struggle to explain stuff. I gave as much context as I could.