Dont know what to do about marriage
Hi Lozza, welcome
I know what he's feeling with sexual incompatibily. Its a difficult one to tackle alone.
Also you crutially need a diagnosis. Depression can effect yoir sex drive big time. See your GP.
Both of these issues need addressing. 23 years is a long time to throw away. Be sure by seeking the help you both need. Then you've done your best
As Tony WK said if I was you I would be having a talk to a GP about your depression and low sex drive. They may have some really good advice on those issues. Because 23 years is a large investment of time and effort. To wind up alone now I know I lost my partner to cancer, which rely didn't help my depression you at least have some one still to talk to.