He has done something wrong. He has lied to you. He is spending his spare time with someone besides you, that is a female. You should call him on this, and do not attempt to spare his feelings, because he hasn't spared yours. If you think, well, I should really kind of tone down what I say to him, because if he knew how I really felt, it might make him feel bad, or hurt his feelings, or feel like I don't love him anymore (trust me, I have done that many many times), he is going to think you are a pushover and he can vioate the rules if he wants and you won't do anything about it. He is overstepping boundaries, but not only that, he is disrespecting you, your marriage and yoru children. I can speak from experience when I say that workplace friendships can turn into more if not careful. I was good friends with my boss, and he eventually developed a crush on me which led to huge problems at work, as well as at home, when my husband found out, even though he knew we were good friends, and he knew I did not return my boss's feelings, it created a trust issue anyway. I did nothing to encourage romantic feelings, but when you spend a lot of time with someone that you like and connect with, if they are of the opposite sex, chances are, a true attraction will develop. Be careful, and know that you don't have to be a doormat. He owes you so much more than an apology. If this relationship were totally innocent, meaning that if he didn't have some guilty feelings for it, then there would be no need for it to be secret. Suggest that he invite her to the house for dinner with the two of you and your children. Ask her nice, but pointed questions about their friendship. Then, hire a babysitter one Friday night and go out with your friends. Do you think he would like or tolerate that? Be wary of people with major double-standards.