My (m40) gf (f40) are moving to a new city. The father(m49) of one of her children is going to move there too

The father of one of her kids has been harassing her for ~10years and just recently she’s semi successfully set some boundaries. He lives about 4 hours from us now but wants to move to the same city <2 mi away when we relocate.He has no one in his life but my gf and their son. He’s an outcast in his own family and has never been able to keep a relationship. He’s alone and super lonely. He lashes out at her calls her derogatory names in front of her kids and threatens to take take their son and not return. In fact he did this once and had him for a year...I’m concerned because he talks about all of us getting together to spend time or go on road trips. It seems to me he is looking at this as an opportunity to be closer to her and her kids and have family like people in his life.I’m not sure what my role should be in this. When he’s 4hrs away it’s pretty easy to keep him at bay. I don’t want this guy near my kids(mine from previous marriage), I want him to find his own life, and more than anything to stop harassing my gf.Should I be a part of their co-parenting meetings? As a support and as a safety mechanism?Should I talk directly with him and let him know my needs and boundaries or do I stay out of it?Do I rely on my gf to set and maintain boundaries? via /r/relationship_advice https://www.reddit.com/r/relationship_advice/comments/j72ptb/my_m40_gf_f40_are_moving_to_a_new_city_the/?utm_source=ifttt