Losing mother in law

My future mother in law has advanced breast cancer that’s spread throughout her body. She hasn’t been through chemo or radiation in a long while because she hasn’t felt well enough. They don’t she will anytime soon either. Last night she went to the er after not feeling good and not being able to move or eat for weeks. She’s battled cancer for about ten years. The doctors said she doesn’t have much longer but we’re not sure how long yet. She’s currently resting there a few days and at the point of fading in and out and they recommended hospice. I’ve never experienced this before. I’ve lost other people to cancer and addiction. My mom and grandmother had cancer and are still alive and I’m grateful for that. I’ve never had to witness someone go so fast downhill though. I’ve been with my partner almost two years. I’m very sensitive and I get emotional. I have to walk away from my partner so I can deal with it sometimes. I can’t imagine the pain him and his family feel having to cope with this so long and finally being told it’s nearing the end. I don’t know what to do other than cry and remind him that no matter what it will be okay and we’re all here to support him. Please recommend ways to get through this and your experiences

Update: got word from the doctor that her liver is failing and she only has 1-3 months so now we begin dealing with the will and funeral for when she passes

11/22 first visit with her in the hospital. Her breathe rate is slowing but we’re all here with her. Her youngest son came home from the navy and he was the last we were waiting on so I think she knows and is happy we’re here. We’re sitting with her in shifts and reminding her we care