till (one's) dying day
For the entirety or remainder of one's life. Till my dying day, I will never forgive him for what he's done to our family. Despite all her doctors' warnings, my grandmother smoked cigarettes like a chimney till her dying day.
till/to/until your ˌdying ˈday
for as long as you live: I swear I won’t forgive her to my dying day!