What is the male equivalent of a mistress?

Because I have one.

When I married my husband I knew that it was a mistake. I was in love with someone else, but I was pregnant and felt like it was the only choice I could make at the time. But as I was saying my vows I knew I was saying them to the wrong person. I have loved this other man for more than 10 yrs, longer than I have known my husband.

My husband is a fantastic, loving, involved father to our 3 yr old daughter. And he is a good husband, but since my heart doesn't belong to him I am unhappy in my marriage.

I find myself considering leaving my husband to be with the other man. My reason for posting this is that I have no experience with divorce. I do not know if I can rationalize my happiness in exchange for breaking up my daughter's home/family. None of my family or friends have ever been involved in a divorce, either as the partners or as the children. If anyone here has any perspective they'd be willing to share I'd appreciate it so much.

I have just admitted to myself that I am considering leaving. I have not given it much thought and really feel like I need some advice/experiences surrounding divorce to give myself an idea if it is even worth considering or if it would be so destructive to my daughter that I should just give up the idea now. I really can't stress enough that my husband is a wonderful father.