Had to unfriend him...

So I have a co-worker that is a really good friend and that is a little mentally slow, but very high functioning. He is engaged and everything. We were friends on Facebook and I just to unfriend him because lately my news feed has been nothing but naked women and things about sex because he likes the pictures and they show up in my feed saying he liked them. It was just getting gross and awkward. It was mostly naked women, sex, Greenbay Packers, and construction equipment. Now, my delema is I know he will come to work Monday and see that I have unfriended him, he likes to keep track of his friends, it's just how he is. How should I go about telling him why without embarrassing him or getting him in trouble with his assistant because she will tell her boss. He lives in a home where they have constant supervision and care and he may get in lots of trouble for it.

* He could get in trouble for it because his parents pay to have him supervised all the time and he shouldn't. He has been in trouble for in appropriate stuff like that before and he isn't suppose to be looking at or doing things with stuff like that.