The pair first revealed their relationship in May 2020.
"It’s the first time we’ve been able to take pictures together because of the pandemic and all that noise, but it’s been a beautiful first time together," Platt told ET's Lauren Zima of posing on the red carpet with his beau. "It means everything and more [to have him here]."
"It's been a very overwhelming rollout, a lot a noise and a lot of stuff, and having him by my side, it makes everything much, much more handle-able and more joyful," the 28-year-old actor added. "I'm very, very lucky he’s here... He makes it all really feel worth it."
Galvin, 27, first revealed his relationship with Platt during a May 2020 episode of his podcast, Little Known Facts. At the time, Galvin said that their friendship turned romantic after he took over for Platt as Evan Hansen in the Broadway musical.
As for the film version of the musical that brought them together, Platt previously told ET that he "felt a lot of gratitude that I was having the opportunity to immortalize the role and finish the journey all the way from creating it in workshops to doing it on Broadway to being in the film."
Like the stage show, the film follows Evan Hansen, an anxious high school senior struggling to find and accept himself following the suicide of a classmate.
"[I felt] so much excitement that this really powerful story that affects so many people when they come see it in the theater on stage is going to get to affect such a huge number of people now that it's a film," Platt said. "Like, just the sheer number of lives that can hopefully be touched by it is so huge."
"I felt some pride," he continued. "Some nerves, of course -- emotionally and mentally, returning to that character. It's kind of a difficult space to be in. Pressure of, like, creating the same performance, carrying on the legacy of the stage performance. Everything wrapped into one, but mostly just really, really excited."
Dear Evan Hansen is now playing in theaters.