Struggle to orgasm with partner

I 21 F struggle to finish with my partner m21. I have to have internal and external stimulation and he does do that but it’s like my body just gives out before I can. When I do it myself it’s within minutes, but when he’s near me and I’m doing it to myself I still can’t. I’ve tried focusing on the moment and not worrying but after an hr you get tired out. I’ve told my bf that it’s not a him issue thats it s a me thing. I have never had an orgasm with any partner during sex or oral/fingering. He’s gotten me there once and that was after over an hour of play.