You can try and research better sex positions that help the girl reach an "O". Maybe you can try foreplay longer to get yourself REALLY turned on if that might be the problem. You know what You like to pleasure yourself so tell you BF how to move and guide him in a discreet way during sex or in a casual talk about sex.
Also, do you enjoy it but just do not orgasm? If so, try to talk to him and say "Baby, i don't know why my body doesn't reach "O" but, it isn't your fault. your very good at sex and i enjoy every second of it."
If that doesn't work and he still feels like crap, you can just fake it. but be careful, if he ever finds out you've been faking it, he will HATE you... faking it really hurts the guy. so. yeah, i recommend the first 3 or 4 ideas i wrote, faking is like, last last LAST resort.