I find people like that more trouble than they are worth. If it is like pulling teeth to get them to open up, why bother? There are so many men out there, why focus on someone who is socially maladapted?
Unless you feel safe with someone who is emotionally unavailable?
If you really really like him, just go over to his place and hang out with him, without talking. Watch movies, or make dinner together. He probably doesn't have many friends, so it would not be like you were interrupting a lot. And he could ask you to leave when he had enough social time. The key is just to hang out, but don't talk too much.
People like this need to be trained to be social again. Just being in someone else's presence in his space is probably all he could handle at first.
Once he is used to you, then slowly start building on the conversational skills. Then start going out and doing things in public.
But this will be like a few years' investment.
That is why it is easier to go for someone healthier.