Dangerous ex possibly contacting me? please help?

[kommando]

I have one ex, and he is nuts. The relationship was volatile, he was extremely abusive & due to possessiveness would imprison me in a cupboard in his basement. I fell hard for my current fiance and left my ex for him. My ex got a new girlfriend and started harassing her on social networks using fake profiles claiming to be me, he even called me threatening me to leave his gf alone. The girl found out it was him and he left me alone after that. Or so I thought.
He would call and make threats to come hurt/kill me using my current address, then it stopped after a while.

On Facebook there is a guy who persistently contacts me, speaking as if we've known each other for a while. I have no idea who it is, but just by his style of writing and prying questions I feel he may be my ex. After investigating his profile I cant tell if it's a real or fake profile. My ex (who previously had blocked me) is friends with this person, he tags him in statuses/videos, claims they train together and things of that sort, but it all seems fake and suspicious.

Its been 3 years since we broke up, im engaged with an infant and I'd hate to think my "baggage" would come back and hurt my family.Do you think my ex is possibly trying to keep tabs or is planning something?