Your struggle is more common with boys than girls but it definitely is not uncommon.
Your habit is hard to break because the act releases chemicals in your brain that are a powerful drug. You can become hooked on it, just like people are hooked on nicotine, caffeine, cocaine, or any drug.
While this may be discouraging, there is hope, but you have to be forgiving of yourself. You may have started this when something was very difficult in your life and you needed comfort or good feelings. Even children masturbate when they discover their body's power to distract them from the hard things in life. Try sometime called active imagination exercise. Imagine your younger self and be sympathetic to her, offer her comfort and encouragement, and forgiveness, then watch how your view of yourself begins to heal and change. Over time, this kind of meditation can bring healing.
Marriage is not a cure for the wound that brought this issue out, but it can give you a good context for your sexuality and the fulfillment of your sexual desires. Don't mistake this as simply high libido. It is a wound which needs healing and overtime will happen.
Though you may often feel unlovable, when you fall, just go to God quickly and let Him love you anyway. It's a matter of patience, patience, and more patience. Eventually you will find peace and healing and you and some wonderful man will make a beautiful family and you can then look back and laugh about this.