Dear Sav,
I'm so sorry for your loss and the depression you are feeling!! Personally, it seems it would be abnormal not to feel some depression after losing someone you loved so much. All of the deaths I have experienced have changed me, and made my anxiety and depression peak for a time.
The important thing, I think, is not to isolate yourself and fall into that deep hole. Spend time outside if you can, with friends and family. I'm sorry you are having trouble in your relationship with your bf - maybe you can take a little time apart, just explain you are having a difficult time right now.
Praying for comfort for you and the ability to remember all the wonderful times you had with your grandma!
Cindy