@akay,
He obviously believed you were the one for him, and he wanted to know that you believed he was the one for you.
Your actions said that you didn't believe he was the one for you (whatever you felt).
When you were with a boyfriend, he respectfully did not pursue you. This says a
lot about his character.
When he came back from serving overseas, he spent the one night with you despite the fact that he had a girlfriend. After that he did not return any calls. This again says a lot about his character.
Basically he wanted something to remember you by because of how much you meant to him... but his nature is loyalty (despite the fact that he slept with you).
I realise you have regrets and want to set things straight, so that you can have peace of mind, but I don't think you've thought through what giving yourself peace of mind will result in (that is, his lack of peace of mind).
Given what he wanted from you (but never got) - If you let him know what you feel for him (what he previously always wanted), what does that result in for him?
Are you prepared to go through all the way with this? Or just tease him with it? What happens if he has kids? Are you prepared to ruin his wifes life? How do you think he'll feel about the hurt he causes her if he leaves? What about the frustration he'll always feel knowing that his wife is keeping him from the love of his life? Who'll he blame that on (even subconsciously) and don't you think that will cause him more unhappiness?
It may be good for your sake, but there are so many ways it can be bad for him.
Either you go all the way and live with the consequences (which has a small chance of eventually being the best thing you've ever had), or you live with the consequences of your actions to date....but don't go half assed and screw his life up (though there is a chance that won't happen...there's a definite chance it will to an unknown degree) purely so you don't have regrets.