Anyone have experience with cancer?

Just wondering if anyone else has had experience with dealing with a loved one having cancer? My Dad was diagnosed with Glioblastoma Multiforme (aka very aggressive brain cancer) in June. He is fighting, but the cancer has taken away most of his vision, some motor skills, and memory. He's very different now. It hurts to see. I often have a really difficult time, emotionally, with it - especially because I don't live at home anymore. I try to see him and spend time with him as much as I can, but it's very emotionally draining and takes a real toll on me. Sometimes my mind starts spinning and I think about losing him and it puts me in a real funk for days or weeks even. I want him to be around forever but I know that's unrealistic - and unfortunately this is a terminal diagnosis. I'm scared of how much time I have left and I'm a mess. Does anyone have experience dealing with cancer? Has anything helped you? Is there anything I can do to make time more meaningful?