Reese Witherspoon brought one to a premiere. Nicole Kidman sat poolside with another in Portofino. Olivia Rodrigo picnicked in the park with one. Andy Cohen recently announced he’s dating one. This summer, private-equity guys are getting an A-list boost. As firms face an exit slowdown and a yearslong fundraising slump, an unexpected wave of good PR has come in the form of paparazzi photos featuring high-profile pairings. The barbarians of buyouts past, it seems, are now the sought-after boyfriends of the beautiful and famous. “If you live in the celebrity bubble, party after party, with the same people—the same 25 people—life gets really…