I think everyone will agree to never talk to your ex GF again.
Take solace that you didn't marry her.
As for your father, now you know he has no sense of family, no integrity, he can't be trusted. Whether you ever talk to him again, it depends on him and you. I certainly would not be friendly towards him for a long time. I would not bother trying to sabotage him and his new girlfriend. Just move on.
Reaching out for advice is good. Talk to your friends. Find something you enjoy doing, perhaps take classes so you can meet new people. You'll be mourning for a while.
Good luck.
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