Friend keeps on getting blocked

So basically, I was playing with one of my friends. We dodged one game, and then that friend got out of my friends list. When that person wanted to add me, they had trouble because they weren't able to find my name until i was able to add them. I wasn't in their friends list and they weren't in mine. So basically, every time one of us signs in and out, that person gets blocked. I don't know what's the problem.