There are number of reasons why sexual desire could decrease in depression, anxiety, any medication ,
thyroid problems, tobacco or alcohol consumption etc.
You also have to understand that marriage go through different stages ..after married for so many years it is usual that penetrative sex decrease but physical cuddles and intimacy , empathy increases.
Please visit a psychiatrist for further evaluation
Next Steps
Consultant a psychiatrist
Health Tips
Remember that Healthy mental and physical relationship is important for mental health of both the partners