Oh Robyn! My heart goes out to you. I've been there and done that! It is not easy but sometimes it is the only way to find happiness. I am assuming you've tried couples therapy, if not that's one more thing to try before you call it quits. In most cases, the two people have lost the ability to communicate and make things work and need outside help.
I found writing to be very therapeutic and I am sure you will solace in reading the stories of others in this community who are on the same boat as you and have found ways to overcome these tough times.