1st - DO NOT MAKE THIS DECISION WHILE HEAD OVER HEAL IN LUV!
2nd - What is marriage to you? What have you defined marriage to be?
What will happen 1 year after you're married. Do you want to be the provider and have her stay home? Do you want both of you to work so you'll have a great home? Do you want kids right away?
What do you want in 5 years into the marriage?
What do you want in 10 years into the marriage?
What do you want in 20 years into the marriage?
Sit with yourself and ask these tough questions. Then re-ask these questions in a week. If you feel confident that you're honest with yourself, then approach your girl. If you're not quite satisfied with your internal question, keep asking and answering yourself untill your confident.
3rd - When you're confident in what you want ... Ask these same questions to your girl friend. BEWARE ... She'll freak and probably start crying thinking you're asking her out!!! Make it clear that this is a discusion only, and you're trying to figure out the "Next Step". Then ask her several times after the first questions
.
If you've evaluated the situation and feel that for the two of you to form a union, you can then you can pre-pair that special occation with the ring, and the right setting to ask for her hand in marriage.
Best wishes.