Not quite boyfriend. Help!

I've been seeing my ex for almost 2 years now. See, we broke up last year in May 2013. We started seeing each other again in September 2013. To this date, we have been inseparable. We literally do everything together. I am 28 and he is 30. I can't imagine my life without him. But, there is one problem. Ever since October 2013, he has refused to ever be my boyfriend again. What I find so weird about that, is that he doesn't want to see anyone else. In fact, he is more loyal to me than any guy I have ever known. He actually wants to see me every day. When his friends ask him to go out to clubs to meet girls, he never wants to go. But it's weird because that was all he used to do before we met. For over a year now, I am the only woman he has ever seen or been with. Yet, he insists that we are not a couple. I definitely know that he loves me. I feel it more than I have ever felt it from anyone else I have ever been with. I don't know why he is doing this. It has been a long time and I just want some sort of security. I want to feel secure in my relationship with him.