When Kimille Taylor agreed to design the interior of a home in Telluride, Colo., in 2013, she expected the job to be business as usual. That was before Ms. Taylor, a New York-based designer, met Steve Morton, the local architect working on the project.

“We got along right away,” Ms. Taylor, 50, said. “It was a really good collaboration, professionally.”

But as the project — the renovation of a church converted into a residence — neared completion in 2016, their conversations about space planning and millwork took a personal turn, and they discovered that they shared more than just a passion for design: They were also crazy about each other.