Ariana Grande continues mourning the death of ex-boyfriend Mac Miller. On Tuesday, a fan shared a video of a livestream that Miller did on Instagram in August. In it, the rapper played Grande’s “R.E.M.,” which appeared on her fourth album, “Sweetener.” After Grande noticed the video on Twitter, she wrote: “He is supposed to be here.” The 25-year-old also thanked the fan for finding the video and posting it. Grande and Miller started dating in 2016, but news of their breakup spread in May 2018. Following the split, the two remained on amicable terms. After Miller died of an accidental overdose in September (due tofentanyl, alcohol, and cocaine), Grande took to social media to share a tribute to the rapper. Read more: Ariana Grande posted a heartbreaking tribute to Mac Miller: ‘I’m so sorry I couldn’t fix or take your pain away’ “I can’t believe you aren’t here anymore,” she wrote after sharing a video on Instagram. “I really can’t wrap my head around it.” The “Sweetener” singer added: “I’m so mad, I’m so sad I don’t know what to do. … I’m so sorry I couldn’t fix or take your pain away. I really wanted to.” Recently, Grande also…