Trust is a sticky issue, because some people learn to trust and to re-trust, quicker than others. As I see it, the only way to prove someone trustworthy or untrustworthy, is to trust them.
I know it sounds crazy, but face it, the only way you're gonna know for sure, is to trust.
I'm not saying be a doormat. NEVER THAT!
Just that if you're going to do this thing, do it!
Start small and give more as time passes, but please don't straddle the fence, with one foot on the side of "no he won't" and the other foot on the side of "yes he will".
Life is too short! For real!
The both of you need to really think about who you are, who you wish to be, and what you want. From self and each other. Only then can you make clear decisions, as to a relationship.