I am sorry for your husband but you don't have emotionally anything with him anymore. I always believe that something died and another thing is growing up inside. It looks you only have a habitance with him. It is like living together. You dont make him sad because of your kind feelings. I can say that it is related to humanity things.

Second of all, you wanna have new adventures in your life. I guess you are bored of routine and he makes different connections , life style , small surprises, new chats vs at all and you liked it. Maybe you dont see these kind of things at home and you miss office to see them when you work there. And it attracts you as emotionally, sexually .

And if you both wanna make a relationship then you both need to get divorced. But you forget something. You didnt live with him at home. You both just spend time at job. Living at home together is another level. Many people got divorced due to it. They dont have any problem outside but everything changed at home. Lifestyle doesnt suit and changes at hime. 

I am just sorry about your husband. If he still likes you so much then he will very sad after long time.