Eloethan, thank you, that's a useful spin on it - that I've already started the process!
I can't feel genuinely negative towards my ex's new wife, she is really nice, and the poor woman has to put up with him, doesn't she?! I'm also in possession of the knowledge that my ex was with her initially because he already knew her and liked her and couldn't be bothered with meeting new people and dating and stuff, when I left him (he told me this!!), which makes me feel a little bit sorry for her. I'm sure he genuinely loves her very much now, and they do appear very happy together (she seems to have quite low expectations of behaviour so probably doesn't mind his tantrums and general grumpiness).
I wouldn't dream of trying to set my kids against him - and ought really to have had the confidence to know that he wouldn't be able to set our son against me if I had tried to get maintenance (I had little intention of it anyway, but he had to be sure!). I've never even told the kids that he threatened to do that!
I've set my Facebook to not show me posts from either of them, so if they put up photos and tag the kids, it doesn't show up on my timeline but I can still see them if I look at my kids' pages though - I don't necessarily want to miss them all. I'd still much prefer not to feel that twinge if and when I do see those photos though. The one that really got my goat was from Father's day, him wearing the 'Grandad' badge from his card and his wife gushing at what a fab grandad he was. Mind you, my daughter's partner's mother and step-dad do that too - and they rarely even see the boys and my daughter doesn't like them much!
Guess I have no need for anyone to comment on what an amazing Granny I am, it's there for all to see!! 
Scooter58, that's unforgiveable, and I can totally understand how hurtful and angry that must make you! I'm sure your daughters know which of you is the better parent!
Susieb755, that is a wise sentiment from your friend!!