To make a long story short: my mom died recently and her last wish was that we keep her death a secret from her dad (my grandpa). I just moved to our ancestral home a few months ago and I am now the one taking care of my grandpa. Physically my grandpa is very strong but he has constant mood swings and is a bit forgetful. He has also has had high blood problems but is now on maintenance medication. It's hard for me to lie constantly to my gramps and always tell him my mom is on vacation or something to that effect. It's also hard for me to break a promise to my mom that i would carry out her dying wish. (there are lots of other details but it will be too long)
What would you do based on what was said above? (Serious answers only please.)