Oh, that's horrible!
But hey: did the guinea pig have a good life before its death?
And this is your chance to spend as much sweet moments with your grandmother as possible (I do wish her speedy recovery, or at least a merciful end).
And about the love interest: I have been there. I too had to go through that kinda shit. But thankfully, life shifts around you, bringing new possibilities. I have successfully managed to stay as far away as possible from that painful love interest, and I am living to the fullest with other love interests and hobbies ^^.
I hope you are doing much better since the week you wrote this. Just remember: all will turn out MUCH better than you'd expect. No matter how long that will take.