(Sorry if its long) I'm under allot of stress. What can I do? Please give me advice.?

im 17 about to be 18 in april. My grandpa is in the hospital because he had a heart attack and broke his hip. 2 years ago I moved 30 mins away from my old school. I had allot of friends there and a gf. My dad left when i was 10 so i just stay with my mom and my 2 brothers and little sis. I also live with my grandma. I flunked out of school at 10th grade because of depression( I was depressed because I moved to a diffrent school and I had problems ajusting) I have to take my ged test next month, and I barely have time studying because I have to clean up after my younger siblings and I also have to deal with my grandmother shouting at me and my siblings. For example She calls us "useless" "animals" "we're not human beings" "crazy" "dnt you have a brain" and other stuff. Alsothe other day before my little sister went to school (she's only 9 btw) my grandma looked at her and called her a masquerade. I cant tell my mom about the things my grandma does because she's usually at work and I dont want to bother her with my complaints, but my mom knows what my granma's been saying and stuff and she talked to her about it but my grandmother dosent listen. Also to make things worse i havent seen my gf of 2 years because i havent seen her once in about 2 years(next month will make it 3) since I moved away. I cant go see and see her because I have to take care of my siblings. I cant ask my mom because she has to work and then go to the hospital to see my grandpa. And I cant drive because I dnt have my licsence yet, and because my mom and I barely have time, because we're bussy. I know three years is a long time to without seeing your bf or gf, and I know if i was with another girl she would of left me alredy. My gf understands what im going through and she says its ok. But I know deep down she's hurting. I just feel so guilty because the last thing I want to do is hurt my gf. I've known her since 7th grade. We've been through so much, and I really dont know what to do