If he creeps you out, he creeps you out.

I would tell him you would like him to quit texting you (return his crappy old printer; they're very cheap now, you can get your own crappy new one :-) as you feel (no one can argue with what you feel!) he is abusing the right, he's not your friend, he's your mother's friend, maybe tell him in your mother's presence.

You do not have to stick around with your mother and her friends/partner, you love her but she is not necessarily who you would choose as a friend. I'd make myself scarce so he loses some interest; I'd make a plan to make some real life friends my own age and get "out and about" and not have as much time to be around him.