Sex help

Patient: “hello doctor, i have a serious problem that drive me crazy.im 20 years old and i used to masturbate since i was young.now i got a girlfriend that shes hot and we like each other like hell.she love me so much and i love her too…but the problem is that i cant cum while having sex with her and this get us upset.i really need help in that.is i masturbate i can cum easily but not when having sex.THANK YOU.

Doctor: