So.. I just found out my partner of 3 years has been cheating for the last 4 months. I found the messages - very explicit sexting along with photos and videos of them each wanking etc. They've met up in person and stayed together overnight 3 times (1 or 2 nights each time) - seemingly no penetrative sex happened because he couldn't get it up at all (has never happened with me), but obviously other sexual stuff happened in person as well as on messages, also meals out / date type things whilst they were staying together. I confronted him with the messages and kicked him out. We're both mid-30s, I have a young child and my partner has been a big part of their life and co-parenting with me for the last 2 years.
I have screenshots of the messages and a log of the phone calls - they didn't speak that much on the phone and most of the content of the messages is just sex stuff. Yet she talks about the fact that they are girlfriend/boyfriend in the messages and his response is very positive to it. She had no idea he was in a relationship. He's now ended things with her - told her he actually has a partner etc. Weirdly he had also been lying to her about inconsequential details, like what town he lived in, what he'd done that day, like he was creating a whole separate existence.
The lies he told me when he was with her are pretty low - twice he told me he was in hospital when he wasn't, and the other time he left me at home horrendously ill with covid. Each occasion left me with a massive burden of sorting things out, and had a huge impact on my wellbeing (even if he wasn't trying to get his end away). He knew the impact being away at those specific points would have on me - I basically spent the whole time working flat out / crying with stress and sadness whilst trying not to blame him as I thought he was ill in hospital, whilst also obviously worrying about his health. Two of the occasions also coincided with really important work things for me, which I didn't do as well as I should have with because of all the stress/work/worry.
This all happened a few days ago and we've spoken on the phone since. He has absolutely no explanation for why it all happened, just says he doesn't know and was was an idiot, which is frustrating given my main question is why. We were both very happy, good communication, great sex life, excited about future plans etc. Now he's absolutely devastated, realising he's fucked everything up for seemingly no reason. He's not in a good place and is seeking mental health support, in part for him to try and figure out why he's behaved like he has.
I know it's still early days, but am I completely fucking stupid for even tentatively considering getting back together at some point? Obviously only after a long process of talking/counselling etc. Things were so good before, both as a couple and as a family - though I know it wouldn't be the same if we got back together.