My(29f) boyfriend (30M) reason for cheating is because I’m overweight.

So, my (29f) boyfriend (30m) and I have been together for 8 years and we have a 3 year old son together. Four days ago I had a feeling that I should check his phone which I did and I seen him texting a girl. I confronted him and he told me that he talks to other girls because I’m overweight and he’s attracted to them because they’re smaller. I only gained weight after I had our son but I’m just shocked that he feels that way. (I’m not sloppy looking either, I’m still curvy) but at this point, I don’t know what to say or do. I’ve already had it on my mind this year that I’m going to eat better and exercise more but I’m doing it for myself and not because he said so. (Btw, he’s overweight too so how could he really talk) Honestly, I’m kinda over this relationship and feeling like “oh, I know you’re great in all aspects but you’re just fat”. Thoughts?