Toni,

It is not adultery, but it is a grave sin that will, if done knowing it's a grave sin with full consent of the will, deprive you of the grace of salvation (we call this a mortal sin). So, in effect, it is like adultery in that the punishment is similar.

Some things, such as force of habit, can mitigate the guilt, but it is still a sin that should be (brought to / mentioned) in Confession before receiving Holy Communion at Mass.