Hey,
I'm interested in why you feel the need to get married, to 'seal the deal'?
I met my partner when I was 17 and he was 20, fell head over heels in love and was pretty certain I would be with this man until I was old and grey! It's now three years on (ok, might comparatively be short period of time compared with other people giving advice, but I feel it's relevant still) and we are still going strong and I still hold a firm belief that we'll spend the rest of our lives together. However, I am very glad that I didn't rush into any more commitment such as marriage because despite our strong relationship, it hasn't been without our ups and downs and moments where we just wanted to get the hell away from each other!! If you throw marriage into situations like those, which are probably just usual little blips as you grow up, I think it adds a whole other pressure on you and might affect the way you deal with little problems like that, and not for the better!
I say enjoy being young and enjoy each other. You wouldn't believe how much you change in a few short years, sometimes I'm quite amazed me & my partner have grown up together in such harmony, as we were both so different to the people we are now just a few years ago!