I'm confident there weren't any others before this year but, in some sense, I think that was more or less a function of opportunity. We were getting our graduate degrees in the same place, taking the same classes and then going home with work up to our eyeballs. He couldn't have pulled it off.
This year our first "real" jobs separated us for a couple of months... and boom. He found an OW.
On DDay, he raged at me that we had done a great job "isolating" him all of these years. I think he was talking primarily about his penis.
But even if we were happy and faithful for most of our M, I can tell you this: when I met him, he was dating another girl and hitting on me. Sometimes in front of her. He tried to kiss me one afternoon when we were just sitting on a bench talking and I ducked and told him off. Told him he couldn't even speak to me about a romantic relationship until he had fully broken it off with her. And, even after he did, I made him wait several months until I would date him. But I should have seen his boundaries were bad right there.
There was one woman I knew he had a thing for early on in our M. I think he would have started something with her if she were receptive. But she had a good head on her shoulders and soon moved away. He kept in email contact with her (and I'll admit I occasionally checked their exchanges). But she kept it above board and he never pushed it.
And in the two or three years leading up to his A, there were two incidents. One involved him trying to spend the night at an old friend's house (a woman) after a ski trip. But I flipped my shit when I he called me and told me his little plan and he had to get in the car and drive home. But he tried.
The second was when we moved out of state for his new job and he went on an orientation trip with a coworker he knew from a previous job. He told me he had his own room. But one night he called and I heard her in the background. When he came back, I confronted him and he admitted they shared a cabin with separate rooms. He said he lied because the employer had made the reservations for them, he thought it would make me mad, but he didn't want to rock the boat.
That coworker was never the same with him after that trip. She stopped taking his meetings. She told their boss she wanted him transferred, etc etc. He got incredibly hostile when the subject of her came up. And this was someone we used to go out to dinner with...
So I wonder if he tried something and got rejected.
Many other women in his office also began having issues with him and quit or requested transfers after I left. So that makes me wonder as well. To some extent, I think it's possible OW might have been the only one who accepted his advances.
And on our anniversary a month ago, another coworker of his called me ask me, among other things, why we really broke up and to tell me his side of the S (all lies) and that she couldn't find him, had been texting him all day and that she was afraid he was off with OW. So, you know, probably another OW right there.
And I can also tell now that some of his previous relationship timelines don't add up.
So I think I lucked out that our life circumstances, and lack of a willing partner, forced him to keep it in his pants for a decade +. We had a good M for those years.
I wish that I had found this stuff out about him and/or put it together years ago-- but I'm glad I more or less ended it immediately and didn't take his blameshifting BS. Good luck to him.