Go read through posts by Maca....
Great place to start.
I'm his wife and in September told him that I was no longer able to pretend to be a mono person. He was forced fairly quickly to come to terms with some changes in our life as the man I also love has been my best friend for 17years, our roommate for 5 or so and is the bio-father of our youngest child.
Maca for certain NEVER considered anything but a monogomous marriage and has had to do some major leaps of thought to come to terms with this new dynamic-but his posts may help you find some ground to work from.
"Love As Thou Wilt"