How do i stop being jealous?

my boyfriend had a bit of a messy past, hes known to be a charmer and without being biast, hes very good looking. hes normally just nice to everybody, but in some of the pictures he gets tagged in its seen slightly differently, its as if hes around girls wherever he is, and theres a few pictures of him kissing girls cheeks, and then one of him where hes sitting opposite a girl really closely, shes leaning on him by putting her hand on his leg and hes got his arm round her. i told him, drunkenly, that it annoyed me, and he said that he understood because if that was me he wouldve flipped.. but then he said �she tried it on with me that night as well�.. makes me worry a little bit, as because hes so nice he gets attention.. and its not him doing it, its the girls. i get really jealous but i NEVER tell him, i just go all quiet and bless his heart he has no idea what hes doing wrong. i dont think its him, but how do i overcome this horrible gut feeling i get?