If he is giving you no reason to mistrust him, then this is an issue with you and not with him. If he's proving he's trustworthy, then what is it in your past that makes you unable to trust?

Although it can be hard to do, depending on your past, you cannot judge people by others actions. Not being able to trust him will push him away.

This is probably something that will take you a long time to resolve. Are you seeing a therapist?