Scared to orgasm

Hello my bf and I been togetger for 4.5 years abd we are both 19. We started having sex last year abd throughout all this time I’ve never orgasm. The sex is great though, I feel an intense pressure build up but i tell him to stop because it feels to intense. This ALWAYS happen. I can’t even do it by myself. I rarely masturbate tho, I grew up Christian, so I never really done it (I’m not anymore). So how do I just take in the intensity? How do I relax?