Elizabeth Wagmeister Senior CorrespondentSPOILER ALERT: Do not read ahead if you have not watched the Season 18 finale of “The Bachelorette,” which aired on ABC on Dec. 21.“The Bachelorette” wrapped up its 18th season with a franchise-first: the dating series, which premiered nearly two decades ago, had its first Black winning couple.Leading lady Michelle Young fell in love with Nayte Olukoya, who ended the season with a televised engagement.