I've been very lucky in that the only real relationship I've had that incorporated elements of BDSM was very open, in terms of communication. This is very important to me. If I'm not comfortable enough with the person to talk about this sort of thing, it means that I don't fully trust them, and if I didn't fully trust them, then I definitely wouldn't be considering adding in any D/S to the relationship at that point in time. It takes me a very long time to trust someone, but if it's going to happen, it does happen.

So, I think that unless he's willing to talk about it, it probably means that there's not just a "wanting to not lose you" issue, but a trust issue. Or maybe it's the same thing. And maybe he does have desires that he is suppressing, and is terrified of them and not ready to deal with admitting them even to himself just yet.

This means that your main task isn't going to be to try to force him to open up more, but to do things that encourage him to trust you more. It's going to require a lot of patience on your part, probably, due to a lot of the things other people have already written, and it's up to you to decide how much time you're willing to give him.

How much can you accept? Be honest with yourself on this, on both sides: make sure that you are being fair to yourself and to him, not just one or the other. How important is having D/S in the relationship at this point? For me, I think it's not as important as it is with others, judging by some of the responses I've seen on other posts, since I'm very good at taking care of those needs myself. It probably helps that I'm a switch and am also very good at keeping paradoxes in my mind.

I also agree with Jim. As an aside to that, try to find out what he does like (and is willing to admit to liking) and do those things for him. That's advice I got from the Five Love Languages (forgot the author, but it's ironically a Catholic priest) and it makes sense. If you see someone else taking the effort to meet your needs, you are more likely to find out what you can do to meet theirs.