EM, if you're reading your husband's e-mails......you obviously don't trust him.
He burnt you once....with an affair.
Seems that it is still on-going, ain't it?
There's 3 ways .....people do their 'thinking'.
1. With their brain.
2. With what's between 'you-know-where'.
3. With emotion. (Such as jealousy, over-possessiveness, greed, etc.)
Yours is No.3. (You read his e-mails, therefore you don't trust him, following the old 'golden rule' of...'once burnt,twice shy'.)
I'm no marriage counsellor, but, when a husband goes else-where it is usually after 'something' he's not getting at home.
Yours did it, with an 'old flame'...for the 2nd time!
That should be telling you all you need to know......to either give him 'something better' ( to keep the 'home-fire' burning).....or move on.
Your choice.