Major Dad, thank you for your service and your sacrifice. I hope you can find comfort with the fact that you are living God's plan, not your own. Seek solace with the Lord and surround yourself with your loved ones and enjoy what time you have left.
The day will come for us all when we are no longer able to do the things we once did. It is a difficult and upsetting realization to many, but it is a fact of life. God bless and keep you, enjoy the times that you have left, enjoy the relationships that you have and glorify God with the voice you have left.