i wish you guys the best but i don't need to post statistics to tell you the rate of failure for marriages that start as young as yours. for now enjoy your youth and being together, in the next few years you both are becoming adults and growing and learning a lot from yourselves, so take your time and don't rush into things like marriage when you may not even have a good grip on who you are individually. seeing as how the divorce rate is sky-high, i'd wait til you're a little older and have a better understanding of what's going on around you before you much such a big decision. congrats though on your success thus far, puppy love is still love
as far as relationships, here are a few tips that i've learned personally, if you can get to a bookstore or library there are TONS of books about building relationships
A) COMMUNICATE COMMUNICATE COMMUNICATE. you have to talk in order to have a good understanding of where you guys are
B) time/space. don't get too clingy or the relationship may start to feel stale, especially since you're both so young
C) don't assume that she'll tell you. women especially are the queens of saying "nothing's wrong" when something really is. learn her mannerisms (for example does she roll her eyes when she's mad at you) there's no such thing as too many questions, knowing is better than not knowing
D)this may not be true in your case but most girls don't like being compared to other girls. they already know you look at other women, that's natural, but don't even do that in front of her, it's disrespectful
E) be clear about what you expect from the relationship (kids one day, monogomy, these kind of things shouldn't be assumed)
i dunno, i'm only 22 so i dunno too much about relationships but i hope this helps