She says the couple are "redefining" what it looks like for a "queer person" to be in a heterosexual relationship.
Pansexual people, like Miley, are attracted to individuals regardless of their gender.
"People fall in love with people, not gender, not looks, not whatever," Miley tells Vanity Fair magazine.
"Relationships and partnerships in a new generation - I don't think they have so much to do with sexuality or gender.
"Sex is actually a small part, and gender is a very small, almost irrelevant part of relationships."
Miley adds that being part of the LGBT community is something she's proud of.
Other pansexual people in similar relationships have praised Miley for using her platform to share a message about modern sexuality.