Previous sexual partner

Hi everyone, it's been awhile!

*trigger warning - reference to rape*

So. I had a one night stand after a particularly bad break up.

Then approximately one month later I got together with my current partner (who I have now been together with for 6 years)

When I got together with my current partner, I knew he knew the man I slept with as a one night stand, but I figured I didn't need to tell him as it was prior to the relationship, and I didn't think that they were too close.
As time wore on in the relationship, I realised that although they were not close, they had known each other pretty much all their lives :/ Although they still don't really see each other at all.
I feel guilty about not bringing it up sooner, and now I've left it for so long I feel like it would be bad to bring it up now, years later down the line. So I have put it out of my mind as best I could.

HOWEVER. Two things have come to pass that have made me start thinking about all this again

For the rest of this message the individual from the one night stand will be referred to as "friend", and my partner as my partner.

I will tell you chronologically what has happened to make this dwelling on the matter occur:
1. A business opportunity that may or may not happen has cropped up, that means me and my partner would not only be together, but would also be working together, possibly for at least a few years. Which on the face of it, isn't an issue, but I started thinking maybe he should know, as if he didn't know but he did then find out about the night with the "friend" after the decision to go ahead with the business opportunity, he may feel trapped and unhappy. Although the business opportunity is only a maybe at this point, it is a very possible maybe, and therefore my brain thought that my partner should have all the info prior to any decision making. Although I am understandably concerned that telling him may sour our relationship, the business opportunity, everything really. Or it may make me finally totally free and easy in my mind, if my partner handles the information well!

2. As if by magic, whilst I was mulling this over, the "friend" messaged me (hasn't messaged me since 2016!) asking if I had ever told my partner about it. We had a conversation (shows his ridiculous state of mind! But it does concern me as I would rather tell my partner myself, than him finding out elsewhere!) which basically informed me that he was high (which is why he was asking) but have I told him (no), he thinks we should tell him together (even though he doesn't know how he would take it), to which I said I'd rather tell him myself if it ever came up, and he then proceeded to say that was fine, but the reason he was really asking was because him and his partner wanted a foursome, would we be interested (no!)

In addition to all of the above, I have in recent years found out something awful about the "friend" in question.
So in the scenario when I slept with him, I'd just broken up with an awful ex partner who cheated on me, &was vulnerable, and the "friend" came round to "check on me" but brought booze, and we ended up kissing then sleeping together. Not a great scenario, but he didn't push himself on me or anything, although he was clearly aware I was vulnerable. My only regret over the situation is that it is now awkward, as I am now in love with and with my partner, and he doesn't know about it.

The awful part is as follows. I had a male member of staff (I'm a manager), that was close to this "friend", as the "friend" (and my partner actually) used to baby sit him.
Well, one week he just didn't show up to work. Not like him at all. He didn't communicate, and he didn't turn up the following week. I was worried about him. I reached out to the "friend" as I wanted to make sure the staff member was OK. The "friend" responded that the staff member was fine, he had just lost himself at the bottom of a bottle.
So, a few weeks later, I received a message from the member of staff, apologising for disappearing, and he then told me the following. He had split up with his girlfriend, and started drinking as it hit him hard. Then his girlfriend had contacted him really upset because she had been raped. And that the "friend" was who had raped her.
Now it's awful, but that led me to question the story. If that was actually true, that she had been raped, or if what had ACTUALLY happened, was the exact same thing that happened to me - that the "friend" had gone to see her after the split, got drunk with her and slept with her, and that she then felt bad, and told her boyfriend/the staff member that she had been raped......

Ugh. So complicated! Do I tell my partner all of it completely, or just that I had slept with "friend" rebounding from my ex, or none of it?

Thank you so much for your reply!
And I'm not concerned about the "friend" really whatsoever. I'm more concerned my partner takes the whole discussion badly and I ruin a wonderful 6 year long relationship because this was something I neglected to tell him earlier.....
I've talked to a friend about it, she thinks I should rip the plaster off and tell him as soon as.
I feel like a coward, but I'm now sitting upstairs in our house worried about going downstairs ... :/

Yeah,
I didn't have the guts to bring it up last night. But I probably will today, as its realistically the only thing he doesn't know about me, and if we are to go into business together I sorta feel he should know and process before making that decision. I'd hate him finding out from the "friend" later on down the line and feeling uncomfortable.
I don't know if that makes sense or not!
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