There's nothing mildly unusual about this story. Donating a kidney is huge, it's like sacrificing a significant slither of your life to someone else. I personally could only ever do it for my own child, I can't really imagine loving a woman enough to give her a kidney, but in theory, if romantically illogical love of shakespearian proportions is possible, I suppose it could happen.
However, if she cheated on me, or even if the love faded a little because she made annoying noises when she ate, I'd immediately want it back, or, more sensibly, I'd want to be massively compensated. Ofcourse.
Suddenly you've half killed yourself and destroyed the quality of what life you do have left for someone you don't even like, possibly hate. It would just seriously drive you insane with rage, I wouldn't be surprised if this becomes the infamous case of that guy who wanted his kidney back, lost the lawsuit, then murdered his ex wife by cutting it out through her ass.