So, DH's dad left his mum nearly 3 years ago for a much, much younger woman (younger than DH). His mum took it really, really hard and is still very bitter about it, she's very close with her ex's family and helps out with their family business, so still sees him on a day to day basis so really has to face the fact that he's with someone else everyday. While she's on talking terms with DH's dad, she has really, really serious issues with his girlfriend- the one he left her for.
The issue is that she doesn't want DH, me, or DD to have anything to do with the girlfriend, which is getting to be a bit problematic as the girlfriend and FIL are in a pretty serious relationship- they've been together for nearly 3 years now and have been living together for quite some time. It looks like she's here to stay, and it's getting in the way of our relationship with FIL. We can't have him over, can't go over to his house, and just today when we invited him out to dinner with us and DH's sister, he said that the girlfriend would have to go along with us as she's feeling left out and her and DH's sister are pretty close so she would find out and be upset. So DH declined.
He's afraid of hurting his mum and I totally understand that. And to be fair, his mum would be HYSTERICAL if she found out. Not upset, hysterical. But at the same time, he's missing out on his relationship with his dad, who is a really nice person despite what he did to his mum. Neither of us approve of what he did at all, but I really think it's time to forgive and move on- particularly when there's an important relationship at stake. The last time we saw his dad in a social setting was at our wedding nearly 8 months ago, and even then he only spent a short time there because his girlfriend wasn't invited. I really don't want DD growing up not knowing her grandfather.
I don't know if I should just leave it as something between DH and his dad (and mum) or if I should step in and push DH to have more interaction with his dad- and inevitably his girlfriend?