need advice.

I recently got out of a horrible situation with my ex so I wasn't planning on dealing with anybody...but this guy came around in my vulnerable stage and he was really nice treated me right opened my door the whole 9. We started dating and got pretty serious, we were good for 3 months straight until one day he started becoming distant and weird and I tried to have open communication with him and he just claimed he needed space. But I'm an expert with finding things out and it turns out he was hanging out with another girl. When I confronted him about it he says he started cheating because he went through my phone and seen texts from my ex (mind you they are old texts from months back before me and him even got serious) I feel like it's my fault but I also feel innocent because I have never been the type to disrespect a relationship I take them very seriously. How would you feel? And what should I do