first of all, relax a little here. I know this is probably a very emotional issue, but if I were in your shoes, I'd try to calm down and stop the worry and instead relax and enjoy the relationship that you have right now.
Yes, it can be very important to have a "perspective in a relationship" but living the moment and being happy are just as important, too.
Without wanting to sound overly rude (I have been, and still are in a long distance relationship, so I know where you are coming from): please be sure that xou don't expect to much from your pretty new relationship (3 months is not that long, really) - your happiness should never ever depend on whether one person is your partner, or not. People often change when exposed to different surroundings and situations and while growing up, it's normal that your relationships change, too. - Simply because you change. Yup, some people marry the people that they date in High School, but many don't, and some of those who do, only do so after years and years of seeing other people in the meantime.
Whether you want to be in a long distance relationship while you are in college is really up to you and your partner, and because I don't know either of you, of course I can't make any predictions here. When the time comes that you head off to college (preferably not on the night before you leave though), you and your partner should sit down and Dicuss whether an LDR would be right for you. - That would mean discussing whether you want to be monogamous or poly, what constitues fidelity for both of you, how you'll deal with the money issues that will come up when you're in an LDR, what you'll do about the loneliness both of you will probably feel while being "single, but not single" and the whole bunch. And to be honest about it.
Some people can handle largly leading a relationship via eMail, icq and the phone and seeing their partner every few months, other people are only comfortable when having real contact with their partner every weekend or whatever else. It depends on you, and on your mate. You decide. Nothing is worse for an LDR as one partner being pushed into the LDR.
For now, my personal recommendation is to really not worry about marriage in a few years, but to enjoy what's happening now and to keep the lines of communications about what happens when you leave open and to openly discuss expectations. So give it time....
and live in the moment.
~spanking new Scarleteen Sexpert~
"Through repetition the magic will be forced to rise."