Should i believe what he says?

Im sure there will be several people telling you that he is just a player and to move on...and I suppose you could look at it like that, but he isn't necessarily being a player. He does seem to want the best of both worlds, being in a relationship and being single. Some guys just want to make sure they still have "game" even though they have been in a relationship for a while. However, he very well could be lining up girls just in case you and him don't work out. He is probably confused right now because this other girl came at a bad time since he is in a relationship right now. However based on what happened between him and the other girl (which I am curious to know how you found) I would say that a reconsideration of your relationship status with this guy is in order. I don't think he is quite ready to date you yet.