Your partner has already explained that this is not a new issue and even with masturbation he requires intense stimulation to achieve an orgasm.
Thus, this has nothing to do with you and you need to stop worrying that this means you are unattractive and ineffectual in pleasing him.
He is comfortable with this as he has dealt with this for a long time. He understands that this is not going to change. You don't and seem to assume (perhaps it's your profession) that you can somehow "cure" him of this.
You can't. Either accept what he has told you in terms of being absolutely sexually satisfied by you even without an orgasm or move on.
It's rather doubtful one can blame so called toxic events on ED (and by the way, aspartame IS nutrasweet).
One might blame the increasing incidence of obesity and early onset diabetes as a potential cause since diabetes often cause neuropathy and nerve damage can affect ones ability to achieve an erection. In that instance, the "toxic" environment involves more of a fast fork, second helpings/super-sizing and a lack of desire to push away from the table as opposed to toxic chemicals.
There's no "epidemic" of ED, despite what the marketers of erectile dysfunction medications imply. Many of the men who use these products do not even suffer from ED; they use these medications more in the line of a "sexual stimulant" with the goal of being "ever ready" so to speak or with the belief that these medications will improve performance ("better living through chemistry" so to speak).