So, to give some context, we were dating for like a year and now are friends with benefits. We were separated for some time, but after a couple of months one thing lead to the other and we ended up having sex. And after that, we have been seeing each other for that.

My problem is, I feel like a complete moron, because we get along really well and have a lot of things in common. And I see that she's pretty. I have a lot of feelings towards her, I think that she's a great partner. But there's something that just... Doesn't feel right

She never was skinny, but when we started dating, I saw her as a really beautiful person. I don't mind if she has a belly or if she's not a fitness model, that's not a problem at all (and even though I exercise, I'm not the fittest guy around). But as time passed, some things got more and more... Noticeable. She gained weight, and even though I tried my best to not think about it and to continue loving her as she is, it started taking a lot of my attraction towards her away to a point where I couldn't see myself with her anymore. I never said to her that she was gaining weight, but I tried to convince her to do exercise together and to eat healthy. She always rejected me, and said that "those things weren't for her". She also has some medical conditions (knee pain, to give an example) that were already present when we started dating, but got worse as time passed.

So, that combined with other differences that we had (related to how much we were seeing each other), made me realize that I wanted to break up. She understood it pretty well

The problem is, we've been fwb for some time, and I still see that about her. I think that now she has gained even more weight, and it kinda worries me. We're still able to have sex because we have pretty good chemistry, and I honestly have fun doing things with her, but that feeling is always on the back of my mind. And I feel like a complete asshole. On one hand, I get that feeling as my brain saying to me that she's not the one. But on the other, I feel like I'm wasting a great opportunity with a great person that could make me happy, for something so trivial... I don't know

And yesterday things got worse, because she asked me if we could go back to be exclusive. So this feeling of rejecting her because of her body and nothing more, got even more intense.

AITA for this? Am I too shallow? I don't know what to think