Edit: "I unfriended you because it was unhealthy for me to check in on you. It was not to send any message. I've tried to give you space to make your choices and not try to manipulate you in any way, and not to push you away. But first I have to take care of myself."
I would just go with something like:
"I just wanted to detach from all that Facebook drama, that's all. I just did it for my own peace of mind."
