To be fair, the only people I've 'known' who have CTB have been members here. So, it's not really quite the same or, so intense I imagine. With them though, even though I still (selfishly) miss them, I have to remind myself that it was their choice to go and I respect that we are all entitled to make that choice.
If it's more a case that you worry that you could or should have done more to stop them, I don't know. Could someone change your mind? Could they really change your life to the extent that you wouldn't want to CTB? I'm not sure all people can be saved.
I think mourning loved ones is always difficult though. I've experienced a lot of loved ones dying by natural death. I'm not sure it's something I've ever gotten over or, even wanted to get over in a way. They are gone. I'll never get to see them again. Why wouldn't I be sad about that? It's natural to miss them.
If it's something you want to fight though. If CTB yourself is something you want to resist then, I think Dot may have a point. I'm sure there are support services out there to help people who are grieving.