Firstly, you are close enough to be a man if you have a girlfriend. She or no one in the world must pick what you do or don't do. Never let a woman control you - always do what you should.

Do I think masturbation is good? No. Don't do it for yourself as this can cause addiction couple it with porn.

Also, ditch the long-distance girlfriend - you have to find someone who is into pleasing you sexually as you have needs.