Very very sorry to hear this... I know we dont "know" eachother at all, but my advice and opinion for you is this..
My closest friend had this happen.. he to swore to her nothing had "happened " between them... I told her to stop being so niave, because she kept telling me over and and over and over, her husband was NOT like that blah blah, and of course in the end it all came out. What your husband is doing is wrong. Even if he hasnt slept with her, (which I find that very hard to believe, men crave physical affection and if they dont get it at home they will seek it elsewhere) but he is still have an "emotional affair" with her. Wrong plain and simple. It sounds like to me you guys could use some counseling, if you have been emotionally detached from him for 8 years that is a long time. He was craving something he wasnt getting from you... BUT he shouldnt have turned to another woman but instead I really think you both should look into counseling because their are children involved too.. and then if that doesnt work then go from there... Marriage isnt always happy jolly times, I have been married for 17 years and we all have our ups and downs. Never has infidelity played a part in my marriage though, but what Im saying is too many give up on a marriage when they "Just arent happy anymore" No one is happy 24 hours a day.. and they always think they will be happier with so and so...
Im really sorry you are going through all this, espcially at such a time in your life. ... if you want to talk more just PM me I wish you all the best!!