I can only speak from what my b/f tells me and that's that he feels very alone. I've told him about this site and how it has help me so much to know that I'm not alone and that it may be beneficial to him. Unfortunately, he's not in a place yet where he feels he can talk to anyone but me and his T. He too feels very lonely despite the love I give him, that our friends give him and my family gives to him. He's just not ready to release that loneliness yet because that would mean trusting other people.
Perhaps that's where your parnter is. It's a very sad thing to watch and all I can tell you is to continue to be there for him and love him. Sooner, hopefully rather than later, he will work himself into a place where he is willing to reach out to others and not hold on to the loneliness.
If you fall down 10 times, Stand up 11.