Sorry this is a little long but it needs a bit of background- I am turning 40 this month. My parents separated (very messy divorce) when I was a teenager. For many, many years I did not have a relationship with my Dad. About ten years ago I decided I wanted to get in touch with him and get his side of the story about what went on when they separated. I told my Mum first out of respect that I was going to try and find him and reach out. She said that was fine, he's your Dad after all. But the very second I did actually find him and got in touch she absolutely blew up, said I obviously didn't love her and my siblings and didn't speak to me for weeks. For the record he was fine when they were together, it's not like he was abusive or anything like that or this might make sense.
Anyway, since then I've been on and off in touch with my Dad but recently we've actually developed a proper relationship. He's very much in my life again and honestly he's lovely. He has absolutely no bitterness or resentment towards my Mum over what happened, he's very much a 'things happen and you move on' type of person. He has a new partner which he's been with for many years. Mum also has a new long term partner. No kids in either of the new relationships I will add.
So, as mentioned, my 40th is coming up. Husband has arranged a small party for all my family and close friends. I don't know if I should invite my Dad. I want to, and I'll feel awful when inevitably all the pictures appear on social media of everyone there when he wasn't invited. Mum has actually said it's fine if you want to invite your Dad, but after she told me it was fine to contact him then only to completely blow up when I actually did, I am concerned if he does come there will be another almighty outburst and the night will be ruined. She has not seen him since they separated 27 years ago but I absolutely feel like she still to this day harbours bitterness and resentment. My siblings are in contact with him via Facebook but have also not actually seen him in person in as long. What would you do?