Mr Characters! :)
When I married - could go more than half a dozen times a day. 'wore her out'
As aging changes I learned a few things: 1st is sex partner must be sexually attractive.
Physical fitness is required.
Alcohol will kill your willy - for several days if you really 'tie one on'
Most important for the marital couple - the have to LIKE each other and also be bluntly intimate friends.
Now push a lot of decades and retired - and stuff is changed and probably still changing.
First - just wouldn't get stiff enough (love the British term: "Stiffy" !!)
So - got a rubber "o" ring (actually first one was off a deceased halogen headlight bulb!) - but ornery to get on/off sometimes.
Found something that is made like a Western Tie - the thing that is like a string with a sliding button the ends go through.
Learned how to get it on and it works great - as long as I can get in the mood.
Tried Viagra - didn't make much, if any, difference. Then Cialis - that works better for me.
Another note - treating your partner right (so as to keep that fire ready to start) is all-day/night job. A few evil or deprecating words can kill her willingness in a heartbeat. Be nice 24x7
We do talk about what we like and help each other with finding the right spots to do whatever. Tried some kinky stuff too - but found it to be too artificial or bothersome to get into. Backdoor - tried it - we both decided it wasn't way over-rated. (in our case anyway)
No bondage or anything causing pain or bruises!!!
One more consideration - (well two) - I had to learn to get over mind-movies of her cheating over 4 decades ago. Took awhile. A long while. . .
#2 - women have (%??) issues with their hardware too - just different. My wife has the beginnings of vaginal prolapse which makes her very self concsious. Told her no worries - as long as I can get my cookies off - I'm FINE!!
Also - we have some toys - some especially for her and a few for me to enhance the "o" ring idea. Also very stretchy to get on to where needed.
Then for some "warmer-upper" we have a

We can take turns with it on each other. Funny fact - one of our cats *loves* a bit of massage also and as soon as he hears the thing running, jumps on the bed waiting for his turn.
Last thing I can think of - absolute cleanliness - we do 'stuff' that would not be fun if BO (or other smells) present.
I have a equivalent to a Bidet in the shower to make sure everywhere is absolutely clean and deodorized.
We don't care to watch/read about pornography. Most I've even see is faked garbage. More interesting (!??) to watch two exhibitionists on a beach @ Ocracoke!
Have you been STD tested given you WS activities? Also, have you got over the whatever she did with whoever so you aren't thinking of that when trying to get worked up?
Sad to read of your issues compounded by her low morality.
Wish you well going forward.