I believe 4-5 inches is the average.. I know for some girls when a guy is 7 inches or more, they do both their hands and mouth. - I don't use my hands for I suck at giving hands jobs. LOL
It comes down to your gag reflexes. You're not going to be able to take it all in overnight. Keep sucking it till you're used to it and that your mouth is well adjusted. - Mix it up with cum, flavor lubes, saliva, pre cum.. Get it sloppy wet.
Don't rush into it. Breathe through your nose, relax your throat. Tilt your head back slightly, have him lightly thrust his c-ock down your throat. The best position for is when you're on your knees and if you get better at it and have mastered it, try doing it upside down on the bed. Also, other positions as well.. Since he's 7.5 inches, I wouldn't recommend letting him face f***ing you though it is HOT..
My ex boyfriend was 7 inches and I did gag now and then but I got it all into my mouth, make it very wet.. When he is about to cum, I would have him deepthroat me and come down my throat so he wouldn't have to pull out and the sensation for him will be amazing because the tightness. I got him to be semi hard so it was easier. Soon I was like "Look ma, no hands" LOL - I take time to warm up and I can begin to feel my throat relaxing. I feel like I have to keep a delicate balance between my breathing, my relaxed throat, and this relentless c-ock that is drilling my mouth..
Your mind will play an important role in this too, you must think "I want to please my man." Something along those lines.
Also, rhythm is important. I'm sure you trust him so he needs to be aware of what he's doing.
Practice! Have fun! Oh by the way, don't use a banana.. It won't compare to how brick hard he will be.