Would your SO leave you if you couldn't have kids?

Tonight, In a theoretical game of "what if" gone bad, I made the mistake of asking my Fiancé what he would do if I ended up being infertile by the time we are ready for kids. (Side note: as far as I know I'm healthy and fertile, though we will not be ready for a baby for about 7 yrs). His response was that he would leave me for someone fertile; even after what would then be almost a decade together. Am I taking  this too seriously? Or is his response to this make-believe scenario as sinister as I feel it is??