My boyfriend told me why he keeps losing his erection

Me and my boyfriend have been together a year and our sex life has always been meh... He can only last a small time. Not because he cums but because he loses his erection. I never get off and I always have to finish with a vibrator. He told me this afternoon that the reason he loses his erection is because he was molested in his teen years and his mom used to tell him God made it happen because of his disgusting sexual urges. His mom had caught him masturbating once and drilled into his head that God had to punish him for his urges which is why he got molested... So he now feels shame every time he gets horny. He is in therapy but he's always been too embarrassed to talk to his therapist about that. I feel really awful. I always thought the issue was me. Does anyone have any advice how to help him get out of his head during sex.