PLEASE first off don't cheat. Even if things don't work out you can still hopefully remain friends.
I understand you when you say that you are unsatisfied, but you do love him & he is your best friend.
Now I may be wrong here but it's nothing against you or there is nothing wrong with you BUT is he looking at too much porn & gratifying himself?
I knew a guy (honest not me) that he became a sexual. He started to use porn to "enhance" his sex life but just got used to doing it by himself. You know the right pressure & speed at the right time that sort of thing.
You have already talked to him what in the world doesn't he like the way it feels?
I have also heard that for some reason it hurts when a guy finishes. I don't know if it's the position or what but he then must see a doctor.
Look at this website
link & see if that helps any.
As hard as it is to do you two must talk.
Good Luck I hope that everything works out ok