My wife and I started to open up sexually while I had work stints that lasted 6 months or more. It has certainly made our marriage stronger and it all started back about 6 years ago and she was home by herself. It was long for us both and she was missing sex and her female boss picked up on it and they started to get close.
Her boss was bi and liked my wife a lot. I came home after 6 months and she spilled the whole story to me in tears. She was in need and we agreed that we would be open with each other at that time and that she could see women only. I spent next year at work after that while she worked and got many pay raises while taking care of boss lady. She actually saved enough for us to purchase our first house and when I came home she quit seeing her and we moved away.
After that it has been some swapping and threesomes over the years. It certainly made our marriage strong.