I certainly don't find it abhorrent, but I would understand it more if you had decided to stay together purely for lifestyle, convenience and security, as friends who loved each other.
I don't quite get how one of you can be in love with someone else, but that relationship can go nowhere, because you have to stay together, and how you're still having sex, even though one of you is in love with someone else and not in love with the spouse.
You say you're not competitive, it's the lack of normal human reaction, no jealousy, no competitiveness, wanting no future with someone you're in love with, being in love with that person but still having sex with the person you're not in love with.
I'd get it if it was just shagging around, or I'd get it if you were more just friends, but what you describe has serious emotions involved , he's in love with another woman, and this is where I struggle to understand it.