Help!

My boyfriend and I made it official a month ago. We have been talking for 3 months and have had sex since the third date. Sometimes he finishes, sometimes he doesn’t, sometimes he can go three rounds and still be hard. When he doesn’t finish he tells me it’s not me and it feels amazing, but he gets in his head and nervous if he won’t finish. Do any of you have tips on how to help him finish if he can’t after he is in his head? I offer to give him a blow job but he said he still won’t finish. Please be honest and help me with this.