I can ejaculate from masturbation but not intercourse what could be the reason for this ?

Very unusual: You certainly have forward ejaculation with masturbation, which is the same mechanism as during intercourse. Semen must go into the bladder by retrograde ejaculation if u experience an orgasm during intercourse. Some medications cause retrograde ejaculation. Do you take some medications in the evening before sex, but masturbate at other times during the day? A urologist might help.