I need to find out why this guy I have been seeing wants but only wants to be a monogamous friend?

I have been seeing a guy I met on personals since November 2006. He made it clear to me he wanted a monogamous friendship but he also wants to be intimate as well. He is somewhat affectionate during , but every time I bring up the subject of taking this friendship to the next step in a relationship he backs off and says he has to have time alone to work things out. He hurts me emotionally when he does that and then all of a sudden he comes back and wants to pick up where we left off. I am very confused and emotionally drained. I cannot get him to sit down and just talk about it. He avoids the subject like the plague. I really like him and want to stay with him but I am unsure what he wants to. Help please.