Vampire Transgression by Michael Schieffelbein
Victor Decimus is a two-thousand-year-old vampire, having last seen the sun when he was a Roman soldier posted to Nazareth at the time of Jesus Christ. In the intervening years, he's learned that there are only a couple rules governing a vampire's existence, but those rules are absolute: (1) Vampires are not allowed to associate with other vampires, and (2) once a vampire convinces a human to take his place as a vampire, he must leave the earthly realm for the Dark Kingdom.
Now Victor has broken both rules. He's sired his human lover, Paul, as a vampire and has stayed behind with him on Earth. The two enjoy an intense life as vampire lovers, living in Georgetown and mingling at their private nightclub, where very little is forbidden. But their transgression is not taken lightly, and agents for the Dark Kingdom are now on the prowl, looking to enforce the rules and, if necessary, punish Paul and Victor by threatening all that remains precious to them.