a "fling" could be a short love (and could be nonsense) relationship with another person. therefore, the "fling" in the statement defines the relationship of the two. It could be that they had a great time with one another and then went their own separate ways. You've got to understand in the first place that they don't have a legal relationship and that the girl can run away anytime she wants to. A "fling" relationship mostly doesn't lasts. :)

a fling can also be known as a one night stand. it just means that it wasn't a serious relationship. a fling is when two people meet hook up and don't bother to call or contact each other after.

A fling is a short, casual romantic relationship. So if someone was leaving (going away), any relationship is probably a fling.

If it was a one night stand (as opposed to something of a continuing relationship) you'd say 'was' not 'is' :)