A few tecniques for getting any person to talk:
Mirroring - if the person says something that might be hinting at more to be said, mirror a word or phrase of what they've said back to you.
E.g., "I had a terrible day today."
"Terrible?"
It's a good one to do, partly because you can get the other person to say a lot without actually adding anything. It's a good way of drawing someone out while remaining neutral in your own approach to the conversation. So everything they say comes truly from them.
Reflecting - similar to the above, only you make your own choice of word.
E.g., "I had a terrible day today."
"It was a hard day?"
It's a way of showing that you're listening and of checking that you understand properly without adding very much of your own judgement to the conversation.
You can reflect anything from one word to whole paragraphs.
Summarizing - when the person has been talking for a while, if you summarize your understanding of the conversation back to them it can be a useful way of checking that you've understood. It can be that you hear a person talk about their stresses and be picking mainly up on their family problems when actually the big issue for them is being short of money. So summarizing lets you check with the person.
Asking questions - the person who asks questions in a conversation controls the conversation itself. Questions drive a conversation.
I cannot work out from your contributions to this thread so far whether you ask him much - perhaps he is shrinking away from too many questions from you or perhaps you don't come forward with questions so he has no stimulus to speak - so use your own judgement in how to use questions.
Note also that while questions open up a person to talk, they can also narrow the person's choice of things to say. So use them judiciously.
Think about using only open questions (ones that start with why, when, where, how and who). Open questions beg any answer but 'yes' and 'no'. That said, closed (yes/no) questions can have their uses. But to be aware of the difference can be very helpful.
The Ware Sequence - there are three ways of contacting a person: via feelings, thoughts and behaviour. Different personality types have different orders in which they like to be contacted. I don't have time or space to talk here about the different personality types and in any case, the information is available online, but it may be worth you trying him with each one.
A person will have an 'open door' mode. Mine is thinking, so I like to get straight into talking about deep stuff without any small talk, but another person might need to start by talking about feelings. If someone comes up to me saying, "Hi Satine! How are you feeling?" then it feels like a waste of time to me. But if I went up to the person with feelings as her open door and said, "Hi. So, do you have any ideas on what we're going to say on this thread?" then they would feel unloved and like I was being cold. Another person might prefer that you go up to them ready to do some kind of activity.
The second part of the sequence is the 'target door'. It's not a good idea to walk straight up to the person and approach them with their target door mode but once you've got into rapport with them via their open door, you can. Mine is feelings. I don't want to give up how I feel until I feel like I'm on the same wavelength as another person, but to someone else their target door might be behaviour. Make sure you contact them via their open door before asking them to do anything!
The final mode is the 'trap door'. Don't try to approach the person with this because you, and they, will get stuck. Mine is behaviour and I'm naturally quite an apathetic person. However, all is not lost with the person's trap door, because all you have to do is get to their target door and stay there with them. They will tend to do their own work on their trap door mode. I don't choose to go out for hikes but my boyfriend has a good brain (meets me at thinking), we fall into rapport together and share feelings (my open door) and from there I can do my own behaviours (when I'm feeling looked after, I'll be busy all day. But he cannot push me and when he does, I dig my heels in so hard I find it virtually impossible to stop.)
I don't know how useful these bits and pieces will be to you, but I think they're all worth trying.
Good luck to both of you and I hope you find yourselves in a warm bed of lovely rapport together soon.