According to Luke [Gospel of Love 1]

Luke Finley, the eldest of four brothers, is a committed serial monogamist. He's all for one woman at a time, but not one woman forever. He knows a lifetime of fidelity just isn't in his genes. But when his latest girlfriend kicks him out--of his condo--the woman he's always thought of as "one of the guys" turns out to be the one woman who can rock his world and make him believe in forever.