I think we all have an image in our minds as to what we want our relationship with our parents to be. I'm willing to bet that 98% of the time, that image and reality are not the same. In you and your Dad's case, the image and reality are wildly and widely different. You've come to the conclusion (and rightly so) that you and your dad can't have a relationship ("we don't like each other anyway"). As helpful as it is to come to that realization, it's so hard. I imagine it's very hard and sad for your mom, too. She loves you both. Be good to yourself, keep your boundaries, grieve as long as you need to.