My D17 isn't talking to my WAH (her choice) and yes he came across as stalkerish for months. Tons of texts that she ignored. His texts were all about him "I miss you. I love you. I want a relationship with you." Those come across as selfish. I think he's backed it way down to just sporadic how was school, happy birthday, etc. She isn't answering and I didn't coach her.
D14 just moved in with him and I've heard from her once in 4 days.
For the moment I've come to accept that this is my new norm. Kids caught in the crossfire and everyone loses.