DS1 his dad is still a twat

[shitatusernames]

DS1 is 18, I split from his dad when I was 17, domestic violence etc, he took me court for parental responsibility etc, never got it as he just stopped turning up, like he also did for contact, I continued to turn up for a couple of weeks as told by solicitor.

17 years on I'm married, 3 more children, DS1 has found his dad on facebook and his girlfriend accepted the friends request, he has not bothered to talk to DS1, it's all her, he's got a tattoo of his name on his arm, and is always talking about him apparently

Now, has she told twat head ex that he's now friends with his son or is he blatantly just ignoring him? And am I right in thinking he's still a twat? I thought it would bother me if he found him but it doesn't, but I can see my son getting hurt by it all.

Escape was not easy, I knew for about a month I was leaving, no one else knew, I left on boxing day, I got into Dad's car, shut the door with DS1 in his car seat and said, I'm not going back, when we get home switch the phone off, and that was it, they'd been waiting to hear that since the day I'd left.