There are several factors to consider"
1. Age of the people envolved. If you are going away to
college and your HS GF is either going to a different
college or finishing HS, odds are both of you are going to stray. The older you are, the more likley it is you will not stray.
2. How long have you been an item. Over a year, maybe. Under a year, not much chance
3. How far apart. NY/LA? Denver/Kansas City? If you are close enough to visit it helps.
4. How long apart. A semester? six week job assignment? Deployed to Iraq for not less than 364 days?
Look at these factors and then ask your self if you would be faithful. Then you will know.
SPECIAL CASE!!
I know several couples who are now happily married after meeting online and having a long distance relationship
before a face to face relationship. Take special note of the before.