Only one- and it was someone I was never with.
It was shortly after I broke up with an ex about nine years ago. She was a close friend of mine, we'd been there for each other during some fairly rough shit during the time prior (I was depressed, she was going through health problems, I was her shoulder, she was a light in the dark). She was on the rocks with her partner, I'd split with mine, she'd suggested we could hook up. I was tempted but I made the decision that it wouldn't be right with me torn apart from a breakup and her still technically involved with someone, it all just screamed a bad idea we'd regret., so I had to turn her down.
Of course, as time passed I realised yeah I was actually in love with her. But with chaos in our lives, there was never a time to revisit that and we kinda grew apart over the years.
We still talk now and then, but we're not in each other's lives as such. I get the impression that ship's sailed and we'll never be like that again. Sometimes I wish it could have been otherwise, but at the same time dwelling on it accomplishes nothing - just gotta move forward with your life I guess.
In terms of partners you broke up with, I have absolutely no doubts and second guesses as to those. If anything, time has only proven me more right - I found out recently an ex of mine is starting a family, and that's just not the destiny ahead of me. I've still got a lifetime of walking the earth ahead of me