What should I do about this guy?

Okay. So this guy, lets call him... Frank. Frank has a girlfriend, and a baby on the way. I know this sounds bad, but I think I'm in love with him. I don't know why either... Anyways. He flirts with me constantly, and slaps my ***, I love it, yes. He said that he doesn't want me to "fall in love" with him. He said, "Promise me that we can be friends, with no attachments... Because that would be awesome." I said sure, as always. Now, the problem is.. I text him and he doesn't really text me back most of the time, I'm uming that this is because he is with his girlfriend. I really want to know what this is all suppose to mean. Obviously, I'm not going to get anything out of this but heartache, right? I just can't bare to live without him.. I'm so insanely jealous of his girlfriend, because I want to be with him so badly. Now is there a solution to this? IF YOU ARE GOING TO SAY JUST TO DROP THE ENTIRE THING, I CAN'T.. I WON'T. I need HELP.