My best friend died in questionable circumstances overseas when we were 19. The full story was never revealed: neither when exactly he died or how(we were told he committed suicide by hanging himself). Which, even though no one had been to the place where he presumably died, is a straight up lie due to tons and tons of evidence confirming that it wasn't possible. The main suspect to many people's minds(myself included) was his father. Beyond the fact that he was(and still probably is) one of the nastiest creatures. The fact that he was the one who started the lie about him hanging himself was a huge red flag to begin with(and a lot more emerging with time). Sadly the only person who could really trigger a further investigation was his mom and she has had mental issues for almost as long as I could remember her so that never happened.

Anyway it's been 12 years and I'm afraid I haven't found a good way to cope with it. The first few years were a nightmare to put it very lightly. But at one point I just learned to live with the thought that he's gone. Which is not to say that I don't think about him every day. It just became a norm for me and while it still bothers me and occasionally keeps me up awake at night, I've kind of accepted it and learned to live with it.

I wish I could give you a less morbid answer but I'm afraid that's the best I can do. Sorry. And sorry for your loss.