Relationships are like a giant spider-web of one-way arrows. You have interest in a few other people, they have interest in a few other people, et cetera. Even when the arrows are two-way, they may be of different thickness, since people may well like each other in different degrees. When you get a two-way arrow, the greatest common interest denominator will generally drive the relationship. In the rare relationship, these arrows are roughly identical to begin with. More often, they will differ, but still be quite workable in some form, even if the greatest common denominator of hookup and marriage is hookup.
The long term high school relation will generally fail after one or two years. However, this will put you in a better position than all those of your classmates who immediately got wifed with some upperclassman/entry mate within the first semester because you'll have much better friends. Regardless of whom you're dating, don't ignore your friends for your relationship.
Long distance relationships can be troublesome, and some people would suggest that you avoid them at all costs. They generally only work when both parties are really committed to the relationship; they pretty much invariably don't work if you're more attracted to your S.O.'s hot body than to their witty banter. They also pretty much invariably don't work out if you're more attracted to your S.O.'s witty banter than to their hot body. Don't date someone at home while you're abroad; the results will be disastrous. Even if you're happy at school, leave it while you're away and come back when you return.
Neither girls nor boys make sense.
If at all possible, avoid getting involved (whether in a relationship or simply a casual hook-up) with one of your entrymates ("entry incest") or, God forbid, someone in your a cappella group. Imagine spending two or three years having to sing cheerfully next to someone you went through a nasty breakup with, and you'll understand why. Unless you're really, really sure that that nasty breakup won't ever happen, it's probably not worth it. It is possible to date outside your a cappella group. In theory.
Don't feel obligated to actually be in a relationship while here. While some people feel the need to "pretend" to be happy being single, it really does provide freedom and entertainment for extended periods of time. You'll also have more time to study.
The Boston Globe ran an article about Williams relationships. An excerpt:
At Williams, the refrain is that everyone is either "married" -- inseparable from their significant other -- or prone to "hook up" with people in casual, usually drunken, encounters. Or they have no love life at all.
Get tested. When you give blood, they will check your blood, but it might not be their responsibility to tell you results. You can get an AIDS test now in thirty minutes; most other forms can be done by urine sample. It's easy, quick, and probably free at the health center -- there's no reason not to.
This is not exactly an unbiased source of funding for a report of its kind, but it is a rather interesting study nonetheless -- arguably pretty compelling evidence that college women get the short end of the stick when it comes to the hookup/marriage culture at places like Williams. (and of course, sometimes men do, too.) See here.