Terrified to tell my parents the truth

I've been living with my parents as a recluse since 2020, when I started reflecting on things I did when I was 19 (I was a creep, basically) and realized that my past behavior was not "no big deal" like I previously assumed, that I might have traumatized someone for life, and that people would consider me loathsome if they knew.

I came to the conclusion that there was no future for me, that keeping my past hidden was wrong but being honest about it would just result in me and everyone associated with me becoming outcasts, and that the best thing for me to do was just give up on life. My parents desperately wanted me to tell them why I'd become so withdrawn and erratic, but I believed that I needed to keep the truth hidden from them for as long as possible because, however bad it might be to not know, it would be much more painful for them to find out.

I recently changed my mind and decided that I had to tell my parents and try to find a way to live with myself because, even if my fears are true and there turns out to be no hope for me, there's at least a chance that things won't end in the worst way possible like they will if I stay the course. However, I'm having an incredibly hard time following through with this.

I still think there's a very real chance that this will all turn out to be hopeless. I've never really seen anything that proves that's not the case. I think about the people online who encourage people like me to go on living and I question if they just haven't thought about the risks I'd be taking in doing so. I keep imagining my parents being destroyed by the truth and falling apart like I did back in 2020 and it kills me inside.

I keep setting dates where I'm going to tell them and then losing my nerve and failing to go through with it. I'm just so scared.

My guess is that when you tell people it won't go as bad as you think and others will see you for you as a whole - not a loathsome person defined by this single thing. I also guess that you are being overly hard on yourself. Even if it was serious, I can already tell from this scenario that the answer is not to give up on life.
I think it's the right move to tell them, holding all that on your own is a difficult thing to do and I don't believe is a good path to moving forward. You can heal a lot just through sharing it with others, and gain a lot in perspective. My suggestion if you're having a hard time sharing it would be to write out on paper and give it to them. Tell them that you're having a hard time saying it so you needed to do it this way.
Facing all of this and coming to forgive yourself is probably going to be the hardest thing you ever have to do. I encourage you to look at the overall result of what giving up on life would do to yourself and others vs moving forward and living the best life you possibly can. Living a good life (which includes forgiving yourself -mostly or entirely) and putting a ton of good into your part of the world is the best thing you can do and the best path to redemption in your own heart.