Why can't I orgasm/cum during sex?

Okay so when I masturbate I can usually get to a point where I orgasm and it feels good only for like 2 seconds. When I have sex with my boyfriend it feels very good. We've done many rounds but he's the only one that cums. I hate having to keep lying to him and pretend that I'm having an orgasm or cumming when really I'm not. So can someone tell me how I can please cum and orgasm during sex?!