Its amazing that there seems to be no material online for the sole individual trying to cope with psychological ED. I've read a bit about the methods therapists use: sensate focus therapy.
The point is to STOP THINKING. START FEELING.
My recommendation: While being stimulated (or stimulating yourself), repeatedly ask yourself "How does it feel?" OR just say repeatedly (to yourself or aloud) "That feels good." instead of letting your mind wander to thoughts of inability, etc.
I've been doing this for the last week or so, to good results: I usually can't masturbate without visual stimulation, but by paying attention to the feeling of what's happening I'm able to maintain an erection & climax.
I'm hoping I can have this same focus when it comes to actual intercourse, where I have stupidly been so focussed on the outcome (pleasing her & ejaculating) that I forget to enjoy the whole experience, resulting in my ED.
For the young lady, while stimulating your BF tell him he's not allowed to ejaculate, & be sure to ask a lot "how does it feel?" Causing him to focus on the sensations instead of his own thoughts. The rule that he's not allowed to ejaculate will cause him to relax a bit. But really, he shouldn't...at least until you've made serious progress, where he starts focussing on the sensations & less on having an erection, climaxing, etc.
I'm not a Doctor. But based on what I've read, this is method close to the latter stages of psychological ED treatment. I don't know much about the early stages.