How about life saturation...
I have 2 partners, 1 best friend/metamour. We all live together with 3 of their kids and 1 of mine. I work full time...
I am just saturated. Any spare time I have I try to bike, hike, kayak, get the fuck out of the house and away from people... anything.. last thing on my mind is another romantic relationship.
Only thing I could take on is a casual fling.. I have 0 interest in, and 0 energy for another romantic relationship.
I try to put some of my life into things besides romance or relationships. Work is a 3rd of my life, sleep is a .. 3rdish of my life. The other 3rd can't be all about relationships. I need time for myself.. to find my zen.. to huck myself off of mountains and climb a tree.. Helps me keep my sanity to be a better me in my current relationships.