Am I being selfish?

I’ve made a few post on here but this is an update that changes a lot. So all of my life i’ve basically been controlled and verbally abused by my mom/family. I ended up wanting to leave so bad I married a man & he ended up being abusive as well. I finally got away from him , it was a long stressful process getting him away from us ,ended up coming to my moms because she asked us to. She has been verbally abusive as she was when I was growing up, she always talks down on anything I do, & throws my abusive ex husband in my face. I thought she changed, I can’t go anywhere.I don’t have a life, friends or anything. No help ,I work from home & live in a very small town where daycares are full. He will start school next August thankfully but still months away. My mom does love him. Now I have a great job & i’ve been planning out my move somewhere bigger with more resources , PEACE,and a better life for my son& I to move in February , until last week found out she has cancer! Now I am so hurt because I do love my mom so much and I’d feel guilty to leave. They say it is low risk noninvasive that they are watching & doesn’t require much right now but never know. Idk what to do now, I feel I have no choice but to stay in this town& be miserable now. I have siblings that she treats way better, but they have their own lives, idk if they will help much if I wasn’t here. I’m the one that stays to help her. Why does something bad always have to happen when I finally done something right. I feel selfish to even think this way