I'm so sorry. I know how painful it is to hear. And confessions like that taint so many memories.
During our 1 month of false R, STBX admitted to the same, which apparently had happened years before. For me, it made all those years seem like a lie. I think the longer a secret like that is kept, the more it hurts. I mean, how could he lie to me for that long?!? How could he keep a straight face around me? Maybe I'm just a terrible liar, but I don't think I'd ever be able to do it. My conscience would eat away at me..
Just as a warning, I think cheaters usually start small and build their way up to revealing the whole truth. My STBX's affair went from an EA to just kissing to sex only 4 times to sex for only a couple months to sex for over a year. He admitted to "kissing" another coworker as well, and there's no way I believe that was it, but I was gone before he could trickle truth me on that one too..
I think how you reacted to this piece of information is going to affect how much he continues to reveal to you. I'm not sure how we are supposed to keep our composure when hearing stuff like this, but if telling you this sent you over the edge, then I doubt he is going to tell you more for a while. My bet is that he would stop there and clam up and insist that's the whole truth.. But if you are able to remain calm and show him that you can handle it, then he may keep confessing. I know it hurts, but I think you will want the whole truth if you hope to R..
If you ask me, if I know I'm gonna get shot 100 times, I'd rather I got shot 100 times in one night rather than once or twice every few days or weeks. Trickle truth is a slow and painful death sentence when trying to rebuild trust..
But I remember asking my STBX if he had told me everything about 2 weeks in, and really, it was a pretty stupid question. He had been cheating on me for over a year, so how could he have possibly told me everything in 2 weeks?!? There were so many lies, all the holidays, all the "working late" or "going to my mom's" excuses, and the people that knew, etc. Trickle truth is hell, but I think it's necessary for true R.
Big hugs to you. I know this really sucks.. I hope if there's more to tell he does it soon and with a lot of compassion and promises of change..