Luna loves her husband and he loves her, and it doesn't matter to her that he's not interested in sex. She enjoys curling up with him and talking for hours.
Eventually they'll want children, but for now, they're having too much fun going on expeditions. When that changes, they'll go to a specialist.
Sometimes, Luna does want to have sex. She and Rolf have an arrangement about that. He doesn't want to know who she's with, so she doesn't tell him that she also has an arrangement with Harry and Ginny.
Luna loves her unconventional husband, and her unconventional marriage.