Ok, there's quite a lot of positive stuff here...
Firstly, he seems fit and healthy, though it's still worth him seeing a doctor in case there's something.
Secondly, you say there are problems 75% of the time. That presumably means that 25% of the time things are ok, so you know things can and do work ok in the right circumstances... So you work with him in that to understand what went "right" on those occasions. It could be certain times of day or if he hasn't masturbated recently for instance.
Thirdly, he seems to have a high sex drive and wants to express frequently that with you. More often than not on threads, ED is associated with little interest in sex.
Given he has a high sex drive, I wonder if he could simply be masturbating a lot. Without getting into details, masturbation is generally involves very different physical actions to sexual intercourse, even if both involve the stimulation of the penis. If he is very used to getting himself off in a particular way with his hands, then he won't be getting those sensations through PIV sex, however good it is, and may struggle to maintain an erection and come as a result. This will be exacerbated if you're using condoms, as they will reduce his sensation further (as presumably he doesn't use those when masturbating!)
It doesn't necessarily have to be the infamous "death grip" often mentioned here which implies a porn addiction and such desensitisation that he can only come through particularly vigorous wanking with an iron grip whilst looking at extreme porn.
Of course, porn use could make this far worse, particularly if he's banging one out multiple times a day, and you only have sex after he's already orgasmed once or twice beforehand. If you've not spoken about porn - and i doubt whether you have given your communication about sexual stuff seems almost non-existent - there's a very high chance he uses it.
So, there's a lot to be hopeful about here but it does require:
- You both to communicate about this in a supportive and open way
- He needs to curtail his masturbation significantly, and drop the porn (if he uses it)
- Find a different contraception to condoms (assuming you're using them which I guess you are if he's "faking" orgasms.
- he should go to the doctor and get himself checked out. Some Cialis won't hurt either (better than viagra as it works over a much longer period)
If you both do all that, I'm confident your sexual problems will be solved, but YOU MUST COMMUNICATE!