Fresh off his Rookie of the Year award, Dallas Mavericks Cooper Flagg made things Instagram official with girlfriend, Duke women’s basketball center Ari Roberson, on Thursday. Flagg, who led Duke to the Final Four last March before Dallas took him first overall in the 2025 NBA Draft, shared a snapshot of the pair kissing while in Turks and Caicos on his Instagram Story. Roberson, a 6-foot-4 redshirt freshman for the Blue Devils, reposted the photo with two black heart emojis. Dallas Mavericks star and his girlfriend Duke women’s basketball center, Ari Roberson on vacation in Turks and Caicos. Instagram/Cooper Flagg She also shared a TikTok video that showed them doing an online trend, which included moments from their vacation. “Carry on…” she wrote with a kissing face emoji. Roberson is the younger sister of former Oklahoma City Thunder forward Andre Roberson, who last played with the Nets in 2020-21 after six seasons with the Thunder.…