My New Boyfriend Is Sexually Inexperienced. He Is 27 With

My new boyfriend is sexually inexperienced. He is 27 with only one sexual partner and I'm a 29 year old divorced mom from a 6 year marriage although I have only had 3 partners in my lifetime. We have been exclusive for a few months and for the last several weeks have attempted to take things into the bedroom. I am falling for the guy in every other aspect of our relationship except this. He always gets an erection and can achieve orgasm through oral sex but as soon as anything leads to intercourse he loses his erection. I can get it back but he'll lose it again. He has seen a doctor who assures him that everything is completely "healthy" and that it is all in his mind, performance anxiety. I agree. He'll tell me he worries he'll crush me, what angles he should approach, and that he worries he'll come too fast and that I won't enjoy myself. He is a bio chemist and over thinks everything. I have tried letting him take the lead and do what feels comfortable for him and I have played dominate, both without success. How can I help him overcome this? He is amazing at foreplay, attentive, and is a quick leaner so I know that if we can just get through this it'll pay off as he will make a great lover. Although, I would stay with him even if this continues because I really like the guy. I'm mainly worried because it kills him for days afterwards that he didn't "perform." As a partner what are some things that I can do to help a guy get out of his head and just enjoy the moment? Any tips on how to handle this?