I think I understand the urge to do it, since you don't want to hear crap about your dad and missing him and everything- although I'm sure on some level, you do miss him- he was your dad, even if he was horrible for what he did... but personally, for the sake of your mom, if it were me, I'd do it as far away from any holidays that associate with him, as I could, so as not to just totally wreck them.

That's not a bad idea- enough therapy, you might be able to tell your mom with a little more... objectivity? Or at least, be able to better hide the anger. It's going to be hard enough for her to hear it at all, much less when you're still dealing with a lot of unresolved anger over it. Especially if she chooses not to believe it right away (unwilling or unable to). One of you needs to come into that conversation with a level head, and unfortunately, that dog falls on your shoulders.

As for not missing him, I've known others who do still care very much for their parent, even so. Of course, I was never in that situation myself- but my dad was shabby (left my mom); my mother's second husband was horribly verbally and emotionally abusive to her. Not sexual things, but still there are plenty of reasons I have to dislike them- yet I don't. I don't excuse their behaviors, to be sure. But I tend to remember the good things.