Can I trust him?

I have an update on my previous question of "is he a player?" I confronted him about playing me and he said he wasn't and that he isn't seeing anyone else, but he doesn't want a relationship, not just with me, but with anyone. We agreed the was good and he wants to remain friends with benefits. I agreed as long as he agreed that we would stop if he or I began seeing anyone else. He agreed. Do you think he really isn't seeing anyone? Can I trust him that he'll be honest to tell me when he does start seeing someone? Am I too gullible and being taken advantage of?