Need some advice, my mum died last year (lung cancer, very rapid), 2 weeks before DS was born. DS would have been her first grandchild.
6 months after mum died my dad met his new girlfriend.
Now I have no problem with dad dating again, if it helps him then that's great. There were some problems at the time as he was very keen on me and my brother accepting her as one of the family, very pushy about it. Couldn't seem to accept that we were handling our grief in a different way to him, and I felt like dad was pushing the new gf in to being DS's grandmother - which is obviously a sore point when my mum never got to meet him.
Things were bad last xmas (first xmas with DS and without mum) as neither me or my brother wanted the gf there on xmas day. Ended up compromising by us visiting dad on xmas eve (without her there) and he spent xmas day with her.
Anyway, things started to improve, I was feeling happier with spending time around her. It got easier. Then went downhill again, turns out I don't like her much. I find her quite hard work and there were a few reasons why she didn't seem to be doing dad much good.
All came to a head about a month ago, DS has an egg allergy and she tried to feed him something without checking it was egg free first. Now she knew about his allergy, but had evidently decided we were just being faddy about it. (Have since spoken to her and discovered she thinks we'd gone to one of those places where you end up with a list of "allergies" that actually aren't). DH pulled her up on it and pointed out that she was putting DS's health at risk.
She spent the rest of the day sulking and moaning to dad about us being mean to her.
Then later on that day (once we'd gone) she told dad that he should remove all traces of mum from the house and move on. So dad ended it. She also had a go at him because he'd taken photos of DS cuddling my aunt (mum's sister) and one of my cousins, but not her. DS had gone to them because he knows and likes them, he hadn't gone to her (probably because she was sulking). But dad was apparently meant to take DS to her. 
Have to say I was relieved they'd split, and also quite angry at her wanting all signs of mum removed from the house and expecting DS to be handed to her.
Then a few days later dad got back with her.
Now apparently they are happier together than they were before.
Which is not exactly what I wanted to hear tbh. Horrible as it is, I really wish they weren't together.
Problem is now that dad expects her to be at all family gatherings, and I'm a little uncomfortable with that. I know I can't expect him to hide her away, and wouldn't expect that. But we're now coming across situations like;
- DH's birthday (where he'd obviously rather only have friends/family),
- Xmas (which is a hard time anyway)
- DS's birthday
- my 30th birthday
- the birth of my second child
All quite big/significant events where ideally I wouldn't want anyone I don't actually like to be there. I know I need to compromise, but I also know that it's going to be hard to reach a compromise. My dad can be quick to take offence and finds it hard to see others point of view.
I think I was hoping before that this would be shortlived and dad would move on from her, but it's not looking so likely now.
I just need advice/reassurance really. How on earth do I handle this? I don't want to hurt dad, but I also know I have a tendency to put others needs ahead of my own and have ended up making my mental health quite bad recently due to it. I need a way to deal with this if he ends up with her long term.