stop worrying so much. you have no idea what your life will be like a year from now. anything could happen. just enjoy what you have together. you sound young and im guessing this is a new relationship? if you and she are still together in 2 or 3 years and still happy-you can put a ring on her finger then. right now just focus on the present, enjoy what you have. theres nothing wrong with mentioning the future ocassionally "i hope we get married one day" for example but dont make promises that you may not be able to keep.
also stop talking about what will happen if you break up. staying friends is unrealistic as it would be too painful for at least one of you so scratch that idea.
just enjoy each other and have fun
"Don't ask a question if you can't handle the answer".