idk. for me i'd never be able to trust him again. i believe it's very selfish for one partner to do this to the other. he could have moved out and told you he needed some time out in your marriage. that's the least he could do. by going behind your back is a betrayal of trust. a violation of your relationship. meanwhile you were believing everything was ok. i'm sure he was intimate with you both at the same time. the other woman's behavior is also selfish. how could she have been seeing someone who was already married? sounds to me they are both selfish and amoral. his spilling his guts to relieve himself of his guilt after the fact says a lot to me. it wasn't because he put you first in his life. he just wanted to feel better about something he knew was wrong, imho. it's all very exciting to sneak around. he said, i was deceiving my spouse but it's now ok and for you to say, hey it's ok, i forgive you, i trust you, i'm ok with what u did. i know you love me..this is just my spin on it. my mother did this with my father over a 25 yr. span. even tho they stayed in their marriage and he knew about this other man she continued to see the other man even tho she promised my dad otherwise. he was hurt time and again. when spouses go out of their marriage for comfort it says they are seeking out what they don't want at home. they are not willing to work it through but to find a quick fix outside of the marriage. i'm sure others may suggest couple's counseling or whatever but i saw first hand the damage that is done to one spouse to another in spite of the promises and the violated spouse believing the other.
i'm sorry this has happened to you. you deserve better.