This is beautiful! And I'm going to venture to guess that her friends don't have partners who are willing to spend as much time and effort as you in cultivating intimacy, experimenting with new things, and making her pleasure a priority. Women go off sex when they are bored, and don't feel actively desired (I want you specifically - not just to have sex with the one person I'm allowed to have sex with). And if they are tired and frazzled from working a second shift of dishes and childcare, or don't feel seen or valued on the level they deserve, sex is going to seem less interesting.

You are indeed a fortunate couple with a lot to teach other people about how to have a great relationship and a great sex life.