I hope your dad finds some peace. Pride is a sin, but pride does give confidence. I read what you said, and no self pity doesn't warrant a forked tongue, but self loathing is very complex, especially for men.
I wish the best for you, and think your dad is lucky to have a level-headed son around. For as much as you've been going through, you seem rationally cognitive of your situation, and one could easily say you're making your father's life easier...even if he might not say it.
And also, no way dude...depending on what he did, and backslap could very well be warranted. Grabbing a girl's butt is one thing, but creating a feeling of violation, imo, deserves another violation. 3 smacks i think?!?!....4 right turns equal 360 degrees.