I'm so sorry for your mother's passing, anon. It took me and my mother well over a year to completely get through the grieving process. Hardest work I've ever done. I thought I'd seen it all, but Lord knows I'd never seen or experienced anything like that.
If you can somehow get your Dad to see some male friends, or go to grief counseling (what a blessing it is!) which is open to anyone and free in some communities, please do. If you can sit and just be there with him, do. Everything is normal during grief: ranting, crying, outrageous statements, numbness, frustration, anger, everything. It's like your emotional system has the flu. And the heart is terribly broken. It needs time to heal.