I am a 20 year old virgin with erectile dysfunction?

Yes, I am a virgin, its my business... anyway, I am 20 yrs old, I am getting very close with this girl. I am in good shape(6'1 190lbs), i have always been well endowed you can say about 7.4 last i remember. for the past few months when i masturbate i cannot get hard barely halfway and i cant even stay hard. i tried everything.,,, at first i figured it would go away and it didn't bother me, now it is really bothering me. this girl is the one and i keep blowing her off its embarrassing. what do i do?! i bought these pills in the store by me, it looked something like viagra called "sex booster". i am willing to do anything to get a hard on when i get the chance with her. she has the looks and personality... it has been at least 3 and half months if not longer and i am getting worried. i am also masturbating with less then a half erection, idk if this is good or not(but what am i supposed to do???)... please somebody help me. thank you