Hello Sir, I Am 28 Years Old. I Am Not

Hello sir, I am 28 years old. I am not able to ejaculate inside a girl while having sex but i am able to cum when i masturbate.. 4 to 5 years ago i had an affair an then while having sex with my girlfriend without condom i was able to cum but after her i had sex 3 times using a condom .. and all the three times i was unable to cum while fucking..and while masturbating i am able to cum every night .. please help me out.. i am about to get married and i am very much worried because of this problem.