Hi, I lurk here but rarely post but my partner and I had this problem. I'll just let him type since he doesn't give a shit about my account anyway haha.
Hey, you sound lovely and so understanding. First of all, he's told you the exact reason and its nothing you need to read into any more - performance anxiety (some of the replies here are mental, jesus). Its absolutely not personal or anything to do with you, he obviously really cares about you which is sort of a vicious cycle that can make it worse! I'll tell you what helped for me/us, maybe some of it resonates with your partner. Also I think its very positive that he's up front about it all, that in and of itself is a really good sign that you can work together to fix it!
Firstly, lol at the porn hysteria, though there is some truth in that. This could be harder to broach than the other stuff, but giving up porn completely definitely helped with my sex drive and sensitivity, and can help to break the avoidant cycle. But you don't want to be all 'this is happening just cause you watch porn lol' though I can tell you're not like that at all anyway.
So I think someone else mentioned it but if he's on medication for anxiety or depression like SSRIs, they can really affect erections and sensitivity. Even if he isn't, it brings me to my next suggestion that if he is a bit of an anxious fella in general, look into requesting propanolol for him from the docs. Its non addictive so docs don't mind prescribing it, and essentially whilst (at least in my case) it doesn't stop the mental anxiety, it was fucking amazing at stopping the physical manifestations of it. Surgeons use it to smooth out tremors during surgery and people take it for public speaking etc. Its very good at not letting your nervousness and adrenaline run away with you, which could help perhaps?
Apart from this, my own main issue was that I was always concerned with my partners pleasure, which sounds great but you put so much pressure on yourself (and your partner) that the problems you describe happen. This is very hard to break, and I still get a massive anxiety rush in between just foreplay and once sex is about to happen. What helped massively was just being naked and playing together a lot, with something else on in the background like a movie or whatever. No pressure, no goal, just enjoying each other like that. So its up to you if you want to say (but politer than this lol) 'ok no sex, but lets play for a while' and just see where that leads.
TMI warning ahead I guess ....
Leading on from that, I found sex toys a big help. Again, its partner dependent, he seems nice but obviously be sensitive about the fact its not a case of 'well you're never gonna get me off so here's my colleague Kenneth (peep show reference, sorry) to do the job' but its a 'baby im gonna use my vibrator while you have fun with me and just do whatever you want and feels good because I feel good too' type thing. Just breaking the mental barrier of me feeling like im completely responsible for her pleasure helped a lot. Likewise there's a 'bored and ignored' fetish type thing where the woman does something menial like read a book or watch a movie while the man has his way with her, which obviously sounds like most men's stereotypical dream but if you understand the psychology of removing the pressure to perform its not as terrible/degrading as it sounds and maybe it would help also.
You could also try the tactic that is recommended for men (and sorry if this sounds a bit clinical lol) with delayed ejaculation, where you masturbate together to climax, then once that is achieved you masturbate him to climax, then masturbate a little and let him finish inside you and work it up until normal sex.
Anyway, I guess it sounds like a lot of work, but I think the positive side is that this guy obviously gives a fuck about your pleasure so whilst its detrimental at present if you can get past this stage which I and other users in this thread have said is completely possible, you can look forward to a very exciting and open sex life since you already have great communication and a sex life built on trust and maturity.