I'm fairly new to all of this, but I too can't sleep and this topic struck me.
With him, trust grew from friendship and the fact he's accepted and been nurturing when I've opened up and shared things with him. We've been honest with each other, and since at the very base of what we have is a strong friendship, I know he cares about my well being. I trust him with my physical...and more importantly emotional...well being, otherwise there would be no way I would feel like seeing or opening up to him in anything more than a superficial and safe manner. We're both people, and both need to trust the other, otherwise the risk of getting hurt is to great. To trust each other that we won't hurt the other is the only way to have a relationship.
I don't think I would be willing to put my safety in the hands of someone I didn't trust not to go to far. Because I was abused when I was younger, the threat of lasting mental harm (as well as anything physical that could happen) gives me a cold sweat at the idea of even playing with someone I don't trust. There's just no way. The body heals (for the most part), but the mind always carries scars.