Lots of things can cause sexual “juices” that glow under a UV light (assuming they do, as some of the CSI TV stuff is a teensy bit off). It might be that your SO got herself all worked up into a moist lather thinking about your urgent manhood nestled snugly in her warm basket of love. J’accusing her for that would be unkind.
Cat urine glows under UV light, too. We had an old cat who stopped using her litter box for the last five years of her life (she lived to be 20). After she died, we went through the house with a UV light to find all traces left behind, so the new cats we planned to get wouldn’t get any ideas about where it was acceptable to “do their business”.