Guy problem

Xyhazity
I was talking to this guy for about 2 months now. And I just found out that , he has been talking to this girl who a sophomore (I'm a junior and he's a junior ). I think he just wanted to do the dirty, but I'm not like that. I just feel like it's all my fault that I was pretty enough or skinny enough for him... I just feel really stupid for ever fall for him. And I don't know what to say to him...