My husband makes me so sick, he cheated and now his new girlfriend is being evil. What should I do?

I am deeply saddened. I gave my husband Jerry 25 years of my life. I'm 53 and he's 48. We have two grown daughters together and three grandchildren. I was so good to this man. His entire family LOVED me especially his mother. My husband left me four months ago for another woman and I've been in pain ever since. But we still haven't filed for divorce yet. His mother passed away this morning; she suffered a massive heart attack. She's been ill for a few years and we all knew this day was coming but it's still devastating. My mother in law was so good to me. We all loved her. I'm so upset because I told my husband(that bastard) I'd be there for him when this day comes. I made him this promise long before he cheated on me. I live in Georgia and most of our family lives in Texas. The entire family is crying their eyes out. I called my husband's cell and his girlfriend picked up. Even those this is the whore who stole my husband, I still was polite when I asked to speak to him and she had the audacity to tell me "I am his woman now, it's my job to console him at this time" and then she hung up. Hours later, my husband called me back crying and apologizing for her. I couldn't help it but I cursed him out first THEN I cried with him and offered my condolences. I promised I'd be there for him when this happens and he screwed us both by leaving me for this stupid whore. God bear my witness, when I attend the funeral, this woman better stay far away from me. My daughters and I ALL want to pummel her into the ground. How can I deal with this? What should I do?