It's a very complicated web you're in....love and a roof over your head and poor Grandma, stuck in the middle of nowhere.
I think the best you can do, as you don't want to leave,
is be kind to Grandma, find time, make time, spend time with her, it's her home you're living in, you owe her some perks.
Keep time for yourself too, don't get me wrong, I don't for one second think you should be there....
but you are and you want to stay there for now.
So I would try to make something good of all you have to deal with.
If it doesn't work out, if things get to hard, you must look after yourself first but you have a kind heart and for now you want to live there,
try to take things as they are, see how you feel, don't expect too much of your boyfriend, he is expecting too much of you,
but if you want to be there, you can go with the flow and help poor Gran out too,
but don't take on the burden, it belongs elsewhere.
I hope you manage to find a balance or a new place to live, it's not written in stone, it's your life, you can do whatever you choose. x