FA ex won’t leave me alone & it’s getting weirder

I agree that his gig is beyond FA, and an unequivocal NO should be handed to him directly.  I'm of the mind that the first step there should be a total ceasing of personal communication about feelings and private lives.  That means, enlist friends to have boundaries- a good boundary from the friend would have been a hand up and saying "I will not discuss this with you, it's none of my concern and your association with throwaway is over.  Good day."

No entreaties for space, citing emotional reasons.  It isn't necessary, because the fact is- he lives there now.  He can come and go and see or be seen.  That's the shitty reality.  All that talking to him about it's impacts does is give him some drama to attach reactions to.

I think most attorneys, prior to drafting a letter where no real laws have been broken, is...
"Have you completely blocked him and asked your friends not to talk about him with you?" It's usually first a matter of personal choices and remedial actions that need to be addressed.  The fact is, even though it makes you uncomfortable he is completely within his LEGAL rights to live there, ask his mom about you, talk to people about you.  It may be considered harassment by proxy, to you- but in a legal sense it may not.  It's just weak boundaries on both ends.

You admit that you are still attached to him emotionally, that's understandable.  By this I mean that you don't have full emotional closure and are impacted by things he says and does.  But that also is not a legal issue.  It's painful, but really just seems more emotionally messy than legally questionable. 

I have a belief that when you're done and decisive, and don't have cracks in your boundaries, people go away.  Except in the most extreme situations, and in those there are generally clear violations of law which can be addressed.  Your own emotional strings to this are what give it power.

So yes, I do think that a hard no should be delivered in the form of tight personal boundaries with you and your circle of friends.  But he will still live there- and it's totally up to you if you want to move and get a fresh start.  You can't run from your problems (meaning if you can't make hard boundaries where you are then moving isn't your answer either, you will take your unfinished business with you). However, you can move off the same street as your toxic ex, and might really enjoy the freedom of doing so.

Best of luck- he doesn't sound dangerous to me, he sounds rather pathetic and emotionally manipulative.  I think the threat is the pain it triggers- and that's internal to you.  It's not your fault. Emotions are powerful! But it certainly will be harder to heal without assertive action on your part, whether that's better boundaries, or better boundaries and a move to a neat new landscape.  Whatever it takes, it's nice to have the freedom to choose!