Ugh. :(

I don't know what to do. I've been with my boyfriend for quite a while now. We've made rules like 1. No partying or drugs/alcohol 2. No hanging out with the opposite sex and so on. Anyway, I accidentally clicked on his fb thing and he asked a girl if she was coming back to school. This must mean he notices her right? Also I've seen other convos (not necessarily bad) but some
​Have in the past but when I check later they're gone. I don't want to confront him
​Because it comes off as snoopy. Also, today in his inbox was him
​Asking some guy where the party is at. A month ago someone sent me a picture of him at the party but he claims he only picked someone up. I just can't handle the lying anymore. He just won't change no matter how many chances I give him. I also don't want to leave him because I love him. But he can't even follow the rules that HE made. :( I'm feeling really hurt again. He's also really been starting to irritate me with how he acts.