My boyfriend is avoiding me?

I've been in an LDR with a guy for over a year. We've never really been an affectionate couple but we're each other's best friends, we're constantly laughing or having 4am conversations about life and I love him so much it's unreal. He suddenly started to get really distant, he never really wants to call on Skype and whenever I try to plan to come see him (he's a 3 hour train away) he tells me he's busy. I have to say 'I love you' first and he's getting worse at saying it back but I know he'd break up with me if he wanted to, and he's not. I try to talk to him about it and he avoids it and I just don't know what to do anymore. Advise?