My boyfriend is lying to me please help?

ok so my boyfriend ive been with my boyfriend for over 2 years he quit smoking weed about 2 months ago or so i think he could be lying i dont no what to believe anymore anyways i ask him to stop hanging out with this girl she smokes weed all the time and i dont like her and she doesnt like me so he said ok and hasnt hung out with her for about a year but today i saw a picture on face book that was added yeaterday with him and the girl and other people ive never seen before they are drinking and smoking i dk what they are smoking but thts not what bothers me what bothers me is they were hanging out this isnt the first time this happend we broke up for a day n a half and he had sex with some girl i did things too so dont comment on that i just asked him dont talk to her or hangout with her again he said ok and then i found pictures of him and her and his other friends on face book and one was on christimas and i asked him to come over and he said he was going to his grandmas i confronted him about this and he said sorry i dont think hes cheating but this is really pissing me off i havent confronted him on my recent findings but im going to how far should i take it should i break up with him and how do i stop thinking about it untill i talk to him