Yep, mine cried too, swore with everything he held dear there was nobody else and that his feelings had just changed and he'd not been happy for ages (never once mentioned that, never once gave me the opportunity to change what was making him unhappy, continued telling me he loved me, having sex with me etc etc). I said the exact same thing about 'this would actually be easier for me to understand/deal with if there WAS someone else, looked me in the eye and told me "I know I'm doing a bad thing but I'd never be that bad, I'd never cheat".
And of course there was, actually makes me laugh how predictable it all was now, though at the time it was like a knife to the chest.
Paralysed - I'm not saying "all men", but I can hand on heart say that in every single case I know of (and its depressingly many) where a mans feelings have 'just changed' or he's 'just fallen out of love' there has been another woman/cheating involved. Every single time.
I hate gender essentialism and the whole 'men are this, women are that' stuff but you can't help seeing patterns.
OP I'm so sorry you're going through this.