As others have said, his message is a load of old naval gazing drivel aimed at manipulating you back into line. A few lines that stuck out to me:
I love you and no thinking for a moment it has ever been otherwise.
Apart from the time he performed oral sex on another woman and all the times he kissed her. It wasn't you he was loving in those moments.
I should have told you but I was a coward and worried that I would lose you.
No, he was worried about losing her. Still is.
I am paying for being a wanker putting my short term desire above being a good man. The man I am and the man you married and have loved all these years.
The man you have loved all these years isn't a good man. He's a liar and a cheat. That doesn't change just because he's successfully managed to pull the wool over your eyes for all these years.
Marrying you, having the girls with you, building a life with you I have never ever regretted not once.
Apart from that moment when he saw her walking down the aisle to marry someone else and his carefully crafted mask slipped.
I love my life with my three girls and I don't want to lose it but now it relies on your forgiveness. Don't give up on us.
IE it'll be your fault for breaking up the family.
Honestly. I think you also know her well enough, to know that isn't her either.
Aw bless, defending her honour to the last. What a saint.