What should I do about a weed smoking/lying boyfriend?

He and I have been together for a little over two years. I know he smoked before but he told me he had quit. I believed him but he started doing it and I was angry. But we got ped that because I know how hard it can be to get over an addiction. But he never smoked after that, or at least that's what I thought. He told me last night that he has been doing again for the past 6 moths and thought about leaving me because he feels guilty. He says he is sorry but I don't know what to do. I want to leave him because I caught him saying "Imma start looking for another girl if she dont quit the bitchin" like a year ago to his bestfriend. And then He took pictures with these girls and when i saw it, he lied to me and said that he doesnt know what i was talking about until I showed him the pictures. I really have a hugh struggle with trust even before meeting him. then he pretty much became the oonly one i trusted. I'm so hurt. I told him EVERYTHING, I literally gave/told him everything (house key, money, checks, my parents' financial struggles). I really thought we had an honest relationship. Now he tells me he's really sorry and he wont do it again but I don't know how I can trust him..