Don't hand anyone the key to you heart until they've shown you they can not only keep it save, but give it back when it's no longer deserved.
I relate to this too much. I don't know how to let go. Worse, I know these feelings are unrequited.
Once they have that key, you need to get the lock changed (Ind another)- because you are NEVER getting that key back as long as they possess it. Never.,