Answer:
If he won't show it, chances are that he doesn't love you back. But if you want, just go ahead and ask.
I am going through the same thing right now and a lot of times it's based on a number of things- age, how long you have been together, etc. Have you done something in the past to make him feel like he needs to back away? Or MAYBE he feels like he has tried too hard and is waiting for you to put for an effort. Don't try too hard because you don't want to put forth too much effort and look desperate.. Do some sweet things for him and then if things don't change. Tell him how you feel!