I have major boy trouble?

ok so I moved next to this guy! And since I'm in school i have to walk to his house to catch the bus! Well, we started hangin out although he has a GF! anyhow we were walkin in the field by his house one day and we kissed! He keeps saying he really likes me and cares about me and as long as he gets me hes fine but cant break up with his GF cause he dont want to lose a bet! So at the end of school friday i told him that i couldnt sit around waitin for his GF to break up with him and either way he was losin either me or her! He said that he understood and asked me to give him time to tell her without her cryin. I AGREED! Than at homecomin my friends said he was all over her. IDK what to do! Do I let it go or ask him if he was lying to me? I really like him and i no he likes me. Is he just playin me cause he knows that i will trust him no matter what?