Was Justin Timberlake telling the truth all along? After the singer claimed he only had one drink before he left American Bar in Sag Harbor, leading to his arrest on DWI charges on June 18, the bartender who served him said he did only have “one martini,” they told People. Another employee told the outlet: “If he was drinking more, it wasn’t here.” As OK! previously reported, the 43-year-old star was arrested shortly after midnight on June 18 in Long Island, N.Y., for driving while impaired or intoxicated, the Sag Harbor Police Department said. According to the arrest report, Timberlake told p…