I had a linkedin account and there was one person who i had on my list and we stopped talking and on these accounts you would get a notification on who looked at your profile and noticed that someone would go anonymous and look at my profile and then they kept doing it and i knew who it was so deleted the account as i had no use to it.
Your ex is just unblocking you to see what you are up to then blocking you once done maybe he does this once a month?? he is being nosey and has no intention of contacting you as he was the one to suggest this and its been 3 months now, maybe ask why he does this or just delete his fb once you see him unblocking you.