Honestly....this is ALL I can remember about it. The Main hero was incredibly strong and had various abilities, but he would lose his powers for a day or so after having sex. [and yes, it was a "he"].
This was not the Darkness comic book [Jackie Estacado would die and his powers pass on to his unborn son if he got someone pregnant]. Nor is it Angel:The Series where our Vampire hero couldn't have a "single moment of happiness" or he'd lose his soul.
I don't know if this is a trope of sorts, or if its been done in other shows. so any suggestions to other similar works could lead to the exact show, so... feel free to suggest them.