Part 2: Help! With a Cancer man

I know he cares about me but he must care about his girlfriend too. I'm pretty certain he says he loves her and he's never directly said that to me. He's signed emails with "love" and he tells me I'm very special to him. Aside from the obvious fact that he's being dishonest to his girlfriend by talking to me (and I know that should probably tell me to stay away) I'm trying to figure out his motivation for coming back to me again and again and trying to keep me around.

To me, if I was happy with the person I was with, I would never be talking to someone else like that (and I know he never has in past relationships) but maybe he looks at it differently? Does he not care for his girlfriend that much or is he with her more because she is there and I am not? Are his feelings for me that strong that even though he is happy with her he is willing to risk it to stay with me too? Or is he just having fun having the best of both worlds and getting away with it right now? I know I won't get a straight answer out of him!

Also trying to understand the shifting moods. We will go for weeks where we talk everyday and he initiates the conversations then all of a sudden he goes quiet for weeks where the only time we talk is if I contact him. It's hard not to worry that maybe he's decided not to talk again or is feeling guilty and trying to push away but I'm starting to think that it's just his personality to go through these cycles. So when he's being distant, is it bad to keep sending little "I'm thinking of you" or "have a good day" messages? Honestly it's just my personality to do little things like that because to me it's thoughtful, but maybe he's wanting to be left alone? I could ask but I know he would be too polite to tell me to go away! Any advice? Am I crazy? Should I give up?