Hey! I am very interested in your mans problem.... it doesn't sound like performance anxiety...maybe a little if he thinks he is not performing well, but that thought process is only present as a result of loosing his erection..lost erection happens first THEN feeling bad correct? So I don't think it's anxiety related.. Which is what a lot of doctors will suggest.. He can stay hard for an hour if you give him oral.. So a leak is out of the question and his penis is healthy..
AND you said he doesn't masturbate or watch porn.. So it's not porn induced ED
It's not cholesterol or testosterone... So Im very curious and want to help...
I know you made a point to clarify.. And I don't want you to question his honesty, but are you sure he doesn't watch porn or masturbate? Do you know if he did before he met you and maybe that's a cause for the delayed ejaculation..
But that is weird that it comes and goes...hmm
Anyways here to help