Trigger warning I guess, and sorry for the blogpost

A couple of years I go I found out my father was murdered in a home invasion, stabbed around 30 times. I knew he was dead but I never knew how he died. I was 5 when it happened and the culprit has not yet been found. When I was still a kid but old enough to process death, my mom told me he slipped in the bathroom, hit his head and died. Despite how stupid it sounds now and how blatant of a lie it is, I went with it for most of my life and I'm extremely thankful for it. It allowed me to live my childhood happily, I was outgoing, had lots of friends and actually liked doing stuff. Some time before my 18th birthday I found out about my dad's passing and I've been dead inside since then. I was always a bit pessimistic growing up, but I never realized the difference between thinking something and actually internalizing it, having no choice but to let it eat away at you. I can't remember the last time I laughed or that I felt happy. My dad was dirt poor and his deadbeat alcoholic father abused him for most of his childhood. He worked his ass off, got his law degree and had a bright future ahead of him. Then a roll of cosmic dice decides he has to get murdered in cold blood. This lives in my head like static noise and I don't know if it'll ever go away. I don't go into fits of hysteria over it, nor am I a gloomy faggot, but I've been slowly realizing that I don't actually enjoy anything anymore. I am now 20, I have a beautiful girlfriend and lots of great friends, surprisingly. Rationally, I know my life is going well but deep down I wish I ceased to exist.

I tried therapists and psychiatrists, all to no avail. I talked to my best friends about it, turned to alcohol for a while, nothing worked. I'm curious to hear your take about it, again, sorry for the blogpost. Yes, I heard about Marcus Aurelius and yes, I lift.

TL;DR: dad killed, me depressed, tips appreciated