I disagree entirely with the sexual approach suggested by some. I also don't think that saying you found his things on "accident" is a good idea. Regardless how truly "accidental" this discovery was, it may signal you were snooping around his stuff. The fact is, this is his secret and it shouldn't be yanked out of him. It has to come out naturally. He has already hinted to you that there is something. So, it is perfectly legit for you to ask to have a conversation with him. Tell him how you feel about him, try to make him feel comfortable about the relationship. Trust is a major keyword here. It may take more than one attempt at create a favorable atmosphere for him to feel comfortable enough to finally come clean. Remember, this is something we carry hidden from others our whole lives and it isn't easy to simply blurt it out. This knowledge, once out of the bag, changes lives, yours, his, and the dynamics of the relationship, for better or worse. Handle this with utmost care.