I can't orgasm during sex???

So I've been with my guy for about 3 months sexually and he really turns me on and the sex is amazing but I can't ever seem to orgasm! I can do it masturbating alone but never with him. He has made me squirt and come close but I can't seem to fully cum. He always tells me to just relax and concentrate because he says it's more of an emotional thing for girls and I just have to focus on cummimg until I do.