Friendship

Okay so have this friend who is a guy and we are basically best friends. We have never dated although I'd date him if he wanted to. He always says we are just friends. He recently told me he's talking to this girl and I was perfectly fine with it and everything. This past weekend we went to the same place for a 4th of July day party. He told me I could sleep with him if I wanted. He was going to sleep in the bed of his truck so when we both got tired we went and got in his truck. Well we had sex. It's almost as if he doesn't want to see me with another guy but yet he can be with other girls. I did not bring any of the sex on. He did it all himself. He gets jealous when he hears that I hung out with another guy but he hangs out with other girls all the time.  We have had sex about 6 times. We have never dated. What are your thoughts? Do you think he actually likes me or do you think he just does this because he knows I'll have sex with him?