It can be true. I can relate to the pressure to perform. I've rubbed one out before just so I can last longer later that day.

But in his case it seems like he turned that shit up to 100. He does not seem to masturbate for your sake at all since he doesn't want sex. Still, he may be insecure about his ability to last/perform. Most likely that insecurity is something he grew himself, but try to be careful not to reinforce his doubts.

Maybe you should talk with him about it and make him get counseling. It could be that his insecurities are crippling his ability to perform and be emotionally available and he may be ashamed of his inability to satisfy you (especially since you have a high sex drive, but his insecurities are not your fault) and his porn consumption. If that's true he is just digging himself deeper into that hole.

But maybe he just does not give a fuck or is unwilling to put in effort (hence he doesn't help with your back). I don't know about what's the case here. Just wanted to say, that confidence issues like this may be the issue.