Maybe before he started getting dopamine hits from his work colleague. Or when he started ‘feeling unhappy’ 6 months ago.
I too think he is still cheating. But trying to look innocent. It’s predictable and boring.
Op this is a reflection of him not you. The first person we lie to is ourself. He wants to remain The Good Guy. The one who didn’t cheat. Who did the right thing. But he knows he is not.
Even if he did stay - many marriages break down around 3-5 years later when the person cheated on realises the man they share a home with is just a bit of a loser.
I would never judge anyone for trying to fix the relationship or make it work. But if he remains I bet you will never fully respect him again. Because he has proven he’s unreliable and a bit of a saddo liar. It’s really hard to unsee.
By overstepping with the woman a while back (which I imagine is still ongoing - check the mobile phone bills for the past 12 months - he may be daft enough to phone or text her) he has had to justify to himself why that is acceptable. So he has painted a bleak picture of you, your marriage, his happiness in his head.
We are what we mentally feed ourselves. He will have also had dopamine hits from the colleague. This combination means he knows he’s an arse but he feels wonderful as smoke is being blown up his arse by the woman. So it couldn’t be him - it must be your fault.
My friend’s husband left and part of the reason was the stress of family life and the fact she would like another child.
Now their kids are a bit more independent as they are at school and he is in a smaller rented house, paying maintenance, business folded due to the separation and debts mean his credit is shot and now he has a baby on the way.
She kept the house they owned and has taken on the mortgage after buying him out. I’m not sure he expected this outcome when he was having secret shags during the working day. But here he is.
She looked lovely anyway but has now increased her activity and started sports clubs as she has far more free time. He juggles the 3, soon to be 4 kids every other weekend. Something he struggled with when they were together. I’m really not sure he thought at all about consequences. But he certainly looks run down and not as ‘happy go lucky’.
Choices have consequences - let him sleep in his car (don’t renew his insurance and don’t mention it - let him deal with the consequences of you not being controlling).
But it’s not your fault and don’t feel shame.