I read your post and I laughed. Now,you care about his feelings and that is why you did not block him on Facebook. I think you still have feelings for him and that's why you don't want to block him.
The truth is the guy did not care about your feelings before cutting you loose and bonding with his new girlfriend. I guess he later discovered that the grass is not always green at the other end and that's why he is back again. I'm sure if he is happy in his new relationship, he would not have come back to you.
My advice is never care about his feelings. Block him on every social media their is.Ghost him.Be incommunicado .He will get the message .Don't ever care whether he thinks you are brash or not.To you,he doesn't exist .He was in your past and let the past be. Tell this guy you can never date him again even if he is the only man on planet earth .Block him and stop picking his calls.
Don't ever trust a two faced individual. If you give in,he will hurt you again.A cheat will always be a cheat.