After a year I am still struggling with memories of someone like you. Luckily I blundered into “Adult Attachment Theory” which explains that some adults have a tiny reservoir for intimacy which fills up really fast. They like to attach to adults with a huge reservoir for intimacy because then they can justify to themselves that relationships are too much trouble. And dump their victim. This all happens at a subconscious level so they’re not aware of it. And don’t take responsibility.

Leave him alone. Forget tidying up the loose ends. Be cordial and cooperative at work but get out of his life. Never mind how he is doing. You are not his friend.