How do I keep from crying all the time as I deal with my mother's memory loss from vascular dementia?

I am an only child, and my mom was recently put in a nursing home. (My dad was trying to care for her but couldn't anymore, and I couldn't because I have 3 children and a job.) She remembers me most if the time but seems to know little else. She has gone downhill fast. She had shown signs for a while, and 3 months ago, she was coherent, for the most part. She had a spell 2 months ago, went to the hospital, and she then went to the nursing home for therapy. (She quit walking completely about 2 1/2 months ago. She had been able to get to the bathroom before that with a wheelchair. She has bad arthritis and a spinal problem.) I knew she would never leave. She has really gone down in 2 months...can't even hold a fork, now. I cry all the time, remembering things she said. She said several times that she feared she wouldn't get to see her grandchildren graduate from high school. She cried the last time she said it. I told her, of course, she would, but now, I know she won't. She worried about other things she would never do, too. She and I didn't always get along, but I called her everyday. She was always worrying about me and listening to my problems. I now know she can't do any if this anymore, and I miss that. I didn't always appreciate this, either. She told me a few times that she was the best friend I'd ever have. I now have no one to talk to...my family doesn't understand, and my husband is not an understanding person. I talk to my dad every day, now, but he is not Mom. He listens, and I listen to him, but it's different. I miss my mom, even though she's still here. I will think that I need to tell her something and then realize I can't. It's hard being an only child. I worry about Dad, too. He's dealing with a lot at 84. He does have his mind and gets around fairly well, but I'm afraid he will get sick. What is the best thing I can do to calm down?