Thanks for writing.
Every person’s desire for sex is different, and it can also change over the course of one’s lifetime. Sex drive can also be affected by health conditions, and stress.
Talking to your wife about her health, mental health, and stress may be a good idea.
In terms of having sex by yourself, there are lots of ways to have pleasure on your own.
Another resource is: Jack In World. They have techniques, Q & A, and forums.
Hope this helps! Please let us know if you need any additional information.