Kissing other guys if boyfriend is not being very nice?

my boyfriend of only 2 weeks is flirting wiht other girls...PUBLICIALLY!lol our relationship is secret only me and him know but that is only cause ours families dont get on with each other. but atm he is ignoring me kinda and commenting on other girls pictures saying how fit they are which he knows will annoy me! he is like this though, he was proper in love with one of his girlfriends and cheated on me with her and his next girlfriend he also cheated on me with her. :S urgh i feel horrible but he kinda forced me to..but saying that i didn't stop him after we started :( he was my best friend - friend with benefits almost and i think that now things have gotten serious (in a relationship) its gone all awkward and i hate it. so if i got with another guy do you think it would really matter as he isnt really taking it seriously?