Ok, so as i man of 38, I'm pretty well placed to hopefully give you and your partner some helpful advice.
I developed Peyronies, roughly 4 years ago, and because of this, and alongside my diabetes I began to get mild to moderate ED.
ED for a man, especially at a relatively young age is a viscous circle, what can start as a physical problem can then lead to a phycological problem, which means the normal methods such as PDE5's don't have the same effect.
My partner at the time, gave me very little support and her way of dealing with it was to pretty much not to be intimate with me as she didn't want to feel let down when the inevitable happened and this made it even worse for me from a Psyc point of view.
He needs to establish if its a Physical issue or a mental issue.
Is it a case that he can't get hard, or is it more so that he can't stay hard? If its the former than he has little/no blood flow in, and if it's the latter then he has good blood flow in but poor outflow, effectively meaning the valves in his Tunica don't close - This is where a constriction ring may be of benefit, but ONLY if he has good blood flow in as they trap the blood.
In terms of medications, Vitamins will do F all. Believe me i tried everything and the only things that MIGHT work are PDE5's such as Viagra and Cialis and their retrospective generic names which are cheaper. Neither are prescription only now, and I used to order mine online.
Pills will only work for a period of time, often 2-10 years and after that its injections. After injections, its the implant, which I have, not for my ED but for my Peyronies.
He needs to own it and go get some tests done. Ask for a doppler. This measures blood flow going in and going out. If both are good then its Psychological, and this needs to be addressed completely differently.
Does he have any other underlying health issues? Is he overweight? Has there been a trauma moment for him sexually, either physically or mentally?
A other have said, ED can often be early signs of heart issues, so it is important he gets a diagnosis. ED is no longer the stigma it once was, and ALL men at some point in their lives will suffer from it.
I was depressed and at my wits end, but I sought help and now, with my implant, I can do literally everything better than a 'normal' penis can do and I bloody love it!