When filmmaker Nina Davenport found herself 41-years-old and unmarried in New York City, she refused to let her circumstances prevent her from having a child. In her documentary First Comes Love, which premiered Monday night on HBO, Davenport records her nontraditional journey toward motherhood. Her experience is a testament to that fact that a conventional route to parenthood — “first comes love, then comes marriage, then comes the baby in the baby carriage” — is not necessarily the only path.