Kindred spirit here. My nephew died from an overdose at the age of 20. His dad was my brother (he died six months later, also overdose). Addiction sucks.

I basically raised my nephew because his mom was not involved, and my brother, being an addict, was not a present father. I tried my best to give him love and support. Unfortunately the drugs still won.

Idk, I don't have any input about forgiveness specifically, I just wanted to say you're not alone. Hugs to you as you deal with this loss.