"There is loads of things a man can do even if he has ED, plus it's possible to get Viagra without a prescription from Boots."
JC the point @RamesesCollosus was making seems to have sailed over your head:
"If you were suffering with ED/ impotence and there wasn’t anything you could do about it (as sometimes happens), and your wife was putting pressure on you regardless til you got so fed up with it that you said Look, go and find someone else because I just can’t, how do you think you would really feel about it and what impact do you imagine it would have on your relationship?"
@RamesesCollosusis* *not talking about ED: they're trying to get you to put yourself in your wife's shoes, to understand the situation from your wife's perspective. Do I have to spell it out?
IF (i) sex became unpleasant and painful for you, and (ii) you felt under pressure from your wife to have unpleasant painful sex with her, and (iii) you said in response to that pressure that she could have an affair, and (iv) she then went and had an affair, and she seems to like the guy a lot and fucks him a lot - would you be fine with that?
No? Why not?
Btw, the fact that I had to spell this out suggests you lack the self-awareness needed for basic empathy. THAT is likely where the problem lies in the marriage.
That's also evident from the fact that you want to have sex with your wife even though it hurts her and has been hurting her for a long time - "size has always been an issue". SEX SHOULD NOT BE PAINFUL!
And btw "I don't think that anyone has the right to force someone else into permanent celebacy" - that churlish shit comment indicates that you HAVE been putting pressure on her, because you think you're entitled to have sex. So you coerced her into telling you to have an affair. That is NOT a freely held position, it's a forced one. If you fuck around with this on the table, you will hurt your wife further and the marriage will end, likely not amicably.
Also btw you are NOT ENTITLED to sex with anyone. Not your wife, not with prostitutes (UGH! the majority are trafficked, you'd be complicit to human trafficking), and not with hookups or an affair partner if your wife could be made upset and anxious by it.