How to deal with stress

Sierra • Hope you're having a good day :)
I've had a lot of stress happen to me before and I really didn't handle that well. The past year I've been doing a lot better. But lately it's getting bad again. 
My grandpa, I'm really close to, just got diagnosed with vascular dementia and Alzheimer's. My mum is under stress too and if I try to talk about it to her she starts crying so I hve to be there for her. 
Only two of my classes in school are not honors or college classes. 
My eating disorder is starting to come back but I'm really fighting it.
I have a therapist I see her once a week, I also have a very supportive boyfriend and another amazing best friend. 
I just need help on how I can cope with it and get through it because I cannot depend on everyone