This is a very common question, so thank you for asking. "Separation" has come to have many meanings. Obviously, if a husband and wife physically separate and have separate residences in preparation for a divorce, they are separated as a matter of fact. Husband and wife can also obtain an order from a court that allows them to live apart but be treated as if they were divorced but for the fact that there marriage has yet to be dissolved. This is known as a legal separation. Couples who are legally separated are not divorced in the hope that they may reconcile later. Then there are those like you, who may still reside with their spouses, but have boyfriends or girlfriends with whom they may or may not be having sexual relations. Some people would call this an "emotional" separation, but an emotional separation is usually not considered to be a separation for divorce purposes. Carrying on a sexual relationship with someone other than your spouse while you are still married is not called separation, it's called adultery, and in some jurisdictions adultery can cause you trouble in the areas of child custody and alimony.
Answered on Sep 17th, 2013 at 1:03 AM