Can anyone help to explain and advices

[PassingbyJ]

Sorry to hear about your story.

Looking at it logically, it could be a physical or emotional need.
To girls, its not only about having sex. They could want more foreplay/passion and all other stuff.

It could also be emotional need instead of solely physical needs. Its like just going out once or twice a week doesn't excite her anymore. She could want surprises like those stuff you did during courtship, eg random gifts, outings, dinners, flowers.

It is still possible to savage the marriage, just whether is the effort worth it (depends on likelihood she will stray in future)