03/08/2013 AT 03:00 PM EST
After clocking in at at the Dunder Mifflin Paper Company for nearly 10 years, Brian Baumgartner knows a thing or two about mixing work and play.
But even as The Office
prepares to wrap its ninth and final season, the Kevin Malone actor is still not sick of his colleagues, who make the series' finale a bittersweet goodbye.
"Mine and, really, everyone's life has changed so much over this decade," Baumgartner, 40, told PEOPLE after serving as the grand marshal at Sunday's Subway Fresh Fit 500 race. "We've all grown up together. Our lives have all changed together. We've seen weddings and divorces and kids, success and failure."
And talk about good company: He calls the cast
his "second family." Now, his close-knit coworkers are prepping to film the last episode of the series.
"It will obviously be very bittersweet," he added.
But it's not actually a goodbye, he said. Just a few things on his to-do list: He plays golf with former Office
castmate Steve Carell and tennis with costar Rainn Wilson.
"All [of us] have relationships outside the show," he said, "and that will never change."