How do I [21F] tell [25M] boyfriend about my sexual history?

This is a long story, but to shorten this - I had an extremely strange sexual encounter 3 years ago at 18. I had an *attempted* threesome with a classmate and my best friend, although I was incapacitated and would have never even had sex with the man sober, let alone have a threesome with him and my best friend. (FFM).

My best friend never slept with him, and it was at separate times, although in the same night. I have never sexually touched my best friend. But I did have sex with him.

I am confident that I am dating the love of my life right now. Into our relationship, I initially lied about my body count, as it was 6 before him but I told him 4. I came clean about this unwarranted, and apologized profusely. A lot of my sexual partners have been coerced and I have a very weird sexual history filled with pressure and being under the influence, alongside this instance. I am filled with regret and shame.

I have not told my partner about this, and my best friend is still in my life. However, her partner knows. My partner is a kind man who told me when I told him the truth about my body count that the sexual past is the past, and that he cannot hold the past against. However, I feel as though I have a duty to tell him what happened. I have so much shame for this situation and told my best friend I didn’t want to tell him - but I have to if I want to live a life full of honesty. It could very well come up in conversation.

I am worried he will see me differently, especially since I regret this instance and it does not align with my values regarding sex. I threw up due to how intoxicated I was during the situation, and have so much shame about how this will impact how I am perceived, despite this being years prior.

I’m at a cross roads right now.