Oh, I don't know, I think it sounds pretty universal--friendship is supposed to be give and take, and here you have one person taking all the time while the other person always has to give. In person you say he's great, but if he lives that far away and you only communicate long-distance every month or two, I'm guessing you actually see him in person even less, like maybe once or twice a year. Honestly I might just take the friendship down to "getting together in person once or twice a year" and enjoy that time with him, and then I wouldn't be resentful during the other times when I was struggling to communicate on his terms and his terms only. He sounds kind of selfish to me in that respect and I would rather cut that out of my life, personally, and make him a six-months-only-in-person friend.
I've posted before about my friend Joan, who lives on the other side of the country now. We were really close when we were roommates for years, but once she moved away, I felt like I was making all the effort to keep in contact. I would send three detailed emails about my news and get back one from her, a skimpy paragraph that always began, "Sorry I've been such a bad friend..." Stop apologizing and do something to fix it, was my opinion. Or, drop that label of "friend" down a few notches. I ended up doing the latter because I, personally, was not enjoying trying to maintain the friendship, and I never heard a word of protest from her about it. Now we have contact maybe once or twice a year.
I just had lunch with her when she came through town for the holidays and it was so great to chat with her. It made me a bit sad as I think she's a great person and we could have a good friendship, I think, if she would work on her end to maintain it long-distance, but I don't think it's a priority with her. I admit I did just send her a nice email today, to see if now, after a few years of little contact, she might be interested in reciprocating once again. I'm not getting my hopes up, though. If she said she'd love to keep up but could she call me instead, or IM, okay, I would consider that compromise and try to keep up my end for a while. But I'm at a point in my life where I'm just not going to do all the heavy lifting in a friendship, I don't need or want that extra stress/drama.