Whats up woth my friend and how can I help?

Well, I have a very good guy friend (we're both guys), we click great but there still has always been some kind of ineffable awkwardness between the two of us.

When we first become friends he were much more relaxed, he could be somewhat touchy with me, like pat me on my back, shoulder messages, that kind of sort, or letting our arm or legs touch when we were sitting next to eachother. I have a very cuddly personality so I really do not mind physical contact. Also he were much more talkative before, and he often texted me, at most he could text me 2-3 times each day. Now however, in the last couple of months he has been much more silent and quiet around both me and other friends, and I can't help not to notice that he often looks kind of sad and like he's deep in thoughts. I have therefore, since we are very close friends asked him now and then if he are okey, fine, but always get an empty mutter back that he's good.

So how is he acting towards me now? Well he still glance at me when I'm not looking, and he often linger his eyes at me when we are out with friends. He still invite to body contact when sitting next to me, and usually let some part of him barely touch me when we are sitting next to eachother. But also he seem to be much more reserved when it comes to body contact, and often avoids me or try not to getting too close to me. But whenever he ends up next to me he almost always invite to some sort of physical contact. This behavior are very confusing, it's feels like he tries to avoid me, but if we end up next to each other, watching a movie or something he always use the opportunity to get some physical contact with me. But he does it very discreetly and acts like it is an accident if I notice. If I however play along and act like nothing he would maintain the physical contact. And also he were much easier to talk to before, but now he always seems lost in thoughts and almost depressed when I see or talk to him. But when I get him alone and give him attention he somewhat loosen up a little and become more like his old self. But when we hang out with other friends he always seem to back away and get more invicible, unless I give him some attention.

And to make things even worse his mom helsa a grudge against me and do everything she can to destroy our friendship.
All these make me feel like an emotional wreck, I really want him to get his old joyful self back, but his mother makes thing really complicated. And I really want the old-him back, but then all these question starts; why does his mother hate me, why are my friend so down, why do we get so awkward around each other? Are the problem his mother that forbid our friendship, or are there some kind of sexual tension between us? Or maybe he are depressed because of other caused that I'm not knowing? And of course how do I fix this?