The urologist confirmed nerve damage? Nerves can regenerate, very slowly, under reasonable conditions. It’s been a while since I studied up on it, so maybe someone has better information than me. I know the mental side of this has been mentioned many times in this thread and often in a pejorative manner but it’s worth at least considering that your obvious and understandable distress might in itself be having an effect.
So you’re saying that even with viagra, you find it hard to get and keep an erection?
Try the herbal route. If lack of sensitivity is the problem, then something that can increase sensitivity, horniness and libido may at least work in the short to medium term to combat the symptoms. If it helps, you could maybe go from a combined pill like Male Response, to something a little more targeted to your needs without anything superfluous through trial and error. If it doesn’t help at least you’re only out about £10.
I’m sure the thought of taking a pill at the age of 24 to gain proper sexual function is more than a little perturbing but exploring every sensible route open, hopefully will allow you to taper off later whilst regaining as much of your sex life as possible.
On a different and potentially super obvious note, adding new things to your sex life may help. Maybe things that don’t require your penis but that would help engage the brain in sex: oral for her, bondage, public nudity etc. Things that seem exciting to you.