This will be difficult. Immensely difficult. There's not much that you can do in re-forming his trust in you; you can be the "perfect" girlfriend and have as much patience in the world, but that final push needs to come from him. It will be difficult, for sure, and it will be an uphill battle, but he obviously cares enough to stick with the relationship, y'know? He wants to trust you, and he wants to be with you, but that final push needs to come from him, and you can't blame him for that. You can only be patient. Unless he flat-out states, "I don't want to be with you, anymore," try to assume that he cares, that he wants the relationship to work, and act accordingly. The trust, however, will need to come from him, and it may take a while, but it's not impossible. Just do what you can, if you want this relationship to continue.

I wish you the best.