out of everything you've said... this last part is probably the most important thing to look at.

so you do not believe he'd do anyting to hurt you. you know that there must be a reason that he hasn't been forthcoming entirely with the information so ask yourself what do you think his motivations are? I can't speak to the subject matter but the fact is you're questioning his past also not something in the here and now. So many times things like "the past" have come to cause problems in the present and more often than not, for no good reason.

Ask yourself is the idea that he cares for you as you've laid out, more important to you or that he is entirely 100% perfect in honesty at all times? seriously who is 100% forthcoming with everything especially when it comes to their past and is it realistic to expect that?

is his behavior now something that is on trial or is it something that he did previously and if it's in the past, is yours unblemished too?

I think these are things to ask yourself and ultimately I say again, ask yourself "what's important?"