Also dont put down his mum or her new partner - I know it sucks big time, but you kind just have to take one for the team.
Yeah, that too. My parents separated when I was about 2-ish and I listened to a lot of rubbish. Didn't help me one little bit (even as an adult, I still feel awkward when one parent talks about another). And with my ex, for my eldest daughter's sake, I had to bite my tongue a number of times but it paid off in the end.
Of course I'm not saying you are , or have been, but there might be times when biting your tongue is the hardest thing you've ever done.

And welcome to BB