I was having a light discussion with a friend on the subject of cuckolding and threesomes.
Some people are insanely turned on at the sight of their mate getting it on with someone else. Others get mad, jealous, angry at this scene.
So it translates into 3somes as well: if you don't get turned on by your lover having sex with someone else, you might not like having them bumping uglies in the bed next to you.
As for me, I stop loving my mate when we are having a 3some. Not forever. Takes a day or two to recover. It's probably a defense mechanism to avoid feeling hurt and allowing me to enjoy the experience.
I always found it funny how I can fall in and out of love rapidly. Very quickly.