Sorry it's going to be a tad scripted but this is my guess:
So now he realises he has been caught out and is ''sorry''... after he spent the night possibly not sleeping too well.
He has woken up realising its caught up with him and he cannot have his bit of free and fancy behaving like a single man and then come home to you for dinner as your husband and equal partner in your comfy home.
He has no doubt weighed up his pros and cons and they are not looking too good for him right now.
He is going to start telling you some amazing ''I can change if you give me another chance'' stories pretty soon.
He can start by texting from his phone his bit of fluff in front of you telling her that he doesn't love her, but loves you and was using her.
Then he hands the mobile to you for however long you want it.
However watch him because if he knows the number by heart when he enters it into the mobile, he will just go and buy a pre-paid cheapie and message her again behind your back saying its been a terrible mistake and he is trying to get away from you who has threatened XYZ and poor him, he is worried about the children so is staying put for their sake....
It would be interesting to know if she knows about you...
I am sorry I can only offer you cyber hugs and I feel absolutely gutted for you right now. I think you need to make contact with some good friends and let them know what is going on. You might find they had their suspicions anyhow, but now is the time you need support. xx