Many practitioners have or do incorporate bodily fluids and other organic materials into their spells including saliva, blood, ejaculate, hair, fingernailsm detritus and so on. This may seem disgusting and even taboo to some individuals and cultures, however, common place among some.
It really depends on what you are looking to achieve and in what manner you want to achieve it. If you want to incorporate urine into a love spell there are different methods of doing so. I have read in one instance of someone using their urine in a spell similar to that of a honey jar or witch bottle. I have also read in another instance of someone urinating on someones property to stop them from having romantic feelings toward the person they desired.
Personally, however, urine both physically andsymbolically represent an act of release and cleansing of unwanted material; so using urine in a spell for love doesn't seem like the best choice if you are trying to attract someone. Urine used in spells is more appropriate for getting rid of or banishing something or someone unwanted.