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. 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.
On that note, 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.
The Boston Globe ran an article about Williams relationships here. 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.
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.)