she's usually too tired during the week.
Frank Talk is filled with excellent advice and personal experiences. Those of us in exclusive, long term relationships can benefit. However, in my personal experience, getting and keeping a good stiff erection is at best, only half the battle.
Our partners also age and have problems associated with that aging including sex. I could go into great detail what we have done and what she has done through the years to overcome problems that arise from getting older. Maybe a few of them would be relevant to your situation, but most would not.
It is mostly about compromise between 2 individuals to arrive at a solution benefiting both. Would I like to have sex with my wife 4 or 5 times a week? Of course I would! Using a mechanical means to get and keep an erection makes it doable. Our compromise is twice a week and we are both happy and fulfilled with that.