Would really appreciate some insight on this (girls preferrably), its very important to me.?

I have know this girl for a while and we have a bit of a chemistry. I have slept on her couch on some occasions and am quite close with most of her family. She once looked at me and said, "If you were a couple years older you would have to watch out cause I would be all over you." I was 17 at the time and she had a boyfriend. I am 19 now and she is 23 and single. We are very open with each other, emotionally and physically. I am certain I am in love with her. But about a month ago we were talking, and I said one day I would marry her. She said, "I'm going to hold you to that" and smiled. I am utterly at a loss for what to do haha. I have never had a problem getting girls (although they do confuse the sh*t out of me). I want to be with her more than anything but I really haven't the faintest idea how to go about it with her. And its not like im just some kid, i live on my own, support myself and am going through culinary school and have a great job as a sous chef in one of the finest restaurants in Los Angeles. She is a college graduate and a Law istant at the moment.