This is a form of erectile dysfunction. He is probably looking at himself at the time and has got into a situation of self-fulfilling prophesy. You need to take intercourse off the menu for a while to break this cycle. No performance no anxiety. You take charge, he does nothing.
when one gets over excited, his respiration becomes faster and he gets premature ejaculation. During intercourse, he should breath slow, deep and even( even means, inhalation and exhalation are equal) to do better breathing let him learn abdominal breathing. Googe it.Practice this breathing for 10 minutes twice a day. Then use this breathing while doing intercourse. He can sustain his erection till you orgasm. Breathing controls the mind and mind controls the body.