Facebook is the devil for divorced or soon to be. You will never feel better like this. Try your hardest to find other ways to keep your mind busy, call a friend, read a book whatever it takes. How long have you been separated?

Some people always seem to need someone else.
They are very week and it shows when they move quickly from one to another.
The strong are those that on occasion must go it alone and do. Only to become better on the other side of things. look inside and see the strong person you really are. Life gives us trials to make us better. I would delete him from your friends list. It might not be a bad idea to just not open facebook for a while.

I know how you are feeling in the sense of wondering what the stbx is up to or doing or seeing. As your stbx mine also does not like to be alone and has chosen women that are weak and need someone or use someone. As with me I have and continue to stay faithful because I know I do not need a man in my life when I am finding out who I am and ending a marriage. I always hope karma will knock on his door sooner than later and he feels the pain that he has put on to me and our kids yet that is a waste of energy on my part. It sounds like your stbx is trying to fill a gap instead of hitting reality after all if he had a healthy dose of reality he would feel shame , people like him are not able to hit reality because they have or will do anything to find enablers. Your stronger than that you are in reality and you are learning to deal with it as with him once it hits him he will not know what to do and will be 20 steps behind you while your moving on and forward. Your be ok you just have to put your best foot foward and if you don't know which foot that is try one and if that one does not work out well you have another foot to try. Best of luck.