“Johnny B! Johnny B!” Matt Bomer exclaims as he logs in to Zoom to join his Fellow Travelers co-star, Jonathan Bailey, to do press for their critically acclaimed Showtime limited series.

“Hey, Matty Mo,” Bailey replies.

The actors spent about six months filming the eight-episode series — so, of course, they’ve established a playful bond. On this particular day, they’ve even given each other nicknames.

“I don’t think I’ve ever called Matt ‘Matty Mo’ in my life,” a smiling Bailey says.

“I love Matty Mo,” Bomer replies. “Listen, I love Matty Mo. I appreciate it.”

Bomer and Bailey built a brotherhood and onscreen chemistry for the historical romantic drama about two male political staffers who fall in love at the height of the Lavender Scare, a time when homosexuals were banned from holding positions in the federal government. The series — based on Thomas Mallon’s 2007 novel of...