Anxious about past mistakes

Hi. I'll try not to make this too long or complicated.

Five years ago, I made a mistake that I'm constantly spiraling and ruminating about it catching up to me. This mistake wasn't necessarily "illegal," and it could have gotten so much worse, but it was rather immoral and I feel absolutely disgusted and ashamed of myself each time I remember it. I thought I'd moved on from it until a few weeks ago when it all came back to hit me at once, and since then, I've just been spiraling about it constantly and have been unable to live my life properly anymore. Being scared of what's going to happen is a big fear of mine, and my best friend who knows about this mistake told me that if it's been five years then I really should just stop worrying, but my main problem is how disgusted and ashamed and regretful I feel, and I can't stop ruminating about this mistake on a daily basis.

I don't know what to do anymore. I'm terrified that if I tell people, they will hate me forever, and I'm already terrified of it separating me from the few people that care about me. Do I just come forward and tell those who deserve to know? Do I just move on and accept that what's done is done, and remember that I'm far from the same person I was 3-5 years ago? I don't know what to do. I'm so scared and disgusted and ashamed and I can't stop spiraling about this stuff.