I'm a regular, have name-changed. I had a casual fling with a colleague nearly a decade ago. More of FWB than anything serious, we slept together maybe three times over the course of about 18 months, went out and got drunk together and snogged a bit. We were both single at the time. Both now in committed relationships with other people, there's never been a recurrence.
There was never any expectation on either side that this would develop into a committed relationship (for multiple reasons, not only because we worked together), no-one's heart got broken. All that said, we were fond of each other and it was still, in the nature of these things, a bit tricky in the aftermath going back to a "professional" relationship. We were a bit spiky with one another at work for a bit etc. During this aftermath period, this person told our boss about private discussions we had had while seeing each other which had a direct impact on my pay and advancement. Essentially this information delayed an earlier promotion (I've since made the promotion and it's all water under the bridge). I confronted him and he completely denied he had done this but he was the only person who knew these details so he is the only person who could have told her.
Things are now very normal, professional and cordial: we work well together and occasionally socialise outside work with our partners. No friction at all, never discussed and officially no one at work knows we had a fling (though I think a couple of people suspect). But it's certainly not an ongoing HR or work culture problem.
That said, I fundamentally don't trust this guy to be objective about professional decisions which affect me: he is ruthlessly ambitious, I know he has form for stitching me up and would probably do it again if he thought he needed to.
I'm now going for a promotion at work and have learned that he will be one of 2 or 3 people who decide if I am promotion ready. I had a meeting with my boss last week during which she said this guy would be really central to this process and I should use him as a resource and ask questions about the process.
I'm fundamentally not comfortable doing this. I'm absolutely fine rubbing along with this guy professionally but I don't trust him to have my best interests at heart in relation to a promotion. I need to convey to my boss that I would prefer him not to be involved in decision-making about my promotion, but I don't want to have to tell her why. I don't think the fact we had a fling in itself would be an issue, there's nothing in our work rules which prohibits this, other people have dated at work etc. I just think it would lead to probing by my boss about his character, her seeking to defend him and me looking like a paranoid troublemaker. She is very big on work culture and wanting senior people all to work together harmoniously (which is a good thing) and will need to know what my reasons are for asking him no to be involved. I just don't want to open this can of worms.
Do I just suck it up and accept that he will play a part in this? Or is there another way of dealing with it? We don't in practice have an HR team (we do, but they are in another site and are pretty ineffectual and don't know the history) so I would basically have to speak to my boss or keep quiet and accept whatever happens.