In an interview with the blog Queerty, Mark said that writing Bert and Ernie was based off his interactions with partner Arnold.
"I always felt that without a huge agenda, when I was writing Bert and Ernie, they were," he said. "I didn’t have any other way to contextualize them. The other thing was, more than one person referred to Arnie and I as 'Bert and Ernie.'"
However, Sesame Workshop, which produce the show, deny the fact that they're a couple, saying the puppets have no sexual orientation.
“As we have always said, Bert and Ernie are best friends. They were created to teach preschoolers that people can be good friends with those who are very different from themselves. Even though they are identified as male characters and possess many human traits and characteristics (as most Sesame Street Muppets™ do), they remain puppets, and do not have a sexual orientation,” the workshop said in a statement to NBC News.
The more you know!