It sounds like you understand the situation already for the most part.It's good that you are open enough to accept the possibility of him dating others. So I wouldn't fret too much. Sometimes college brings out a certain sense of need for individuality. Its not the whole "lets have sex freely" feeling as much as it is life without internal boundaries. No matter how accepting each individual is within a relationship, it can take many years and many personal risks before a person can trust themselves to do the things that are right for them without worrying about how their partner feels.
But no worries, sounds like you've got a good head on your shoulders. Chin up and don't worry, just cross each bridge as it comes like you are doing now.
-------
I'm known as Mage and you are?.. You're Someone?.. Pleased to meet ya!