I don't have any advice like Gala Girl does, but I do empathize, since my bf is married (they've been together about 30 years) and he and his wife have sex extremely rarely (as far as I can determine, 4 times a year tops). He also lives and sleeps in a cabin on their land, and she lives and sleeps in the main house.
They do have a ritual of reading out loud to each other every evening, and playing a board game, and they usually take a walk together every morning, plus work on their cars, the washing machine or whatever other home repairs they need to do. Plus they are co parents of their 2 sons. They also often grocery shop together, take each other to medical appts as needed, things like that.
I don't feel threatened in any way by their relationship. *shrug* I don't know why I would! I see Ginger at least once a week, often twice, we have tons of sex, we go out on dates, he helps me with MY home repairs, sometimes he brings me flowers from his gardens. We talk, we cuddle, we go dancing, I love to listen to him play guitar and sing. Any needs he doesn't meet, I have met by my live-in gf, miss pixi. Or I meet them myself. Or if I feel the need for any more attention, I flirt with boys on ok cupid.