Typically performed by someone who is not loyal. They
will constantly move around looking for the 'next best thing'.
If you date an overlapper, you need to constant look over your shoulder. It doesn't matter how much you tell them that you love them, they
will immediately and without warning start dating someone else. If they are a coward, they
will break up with you and give you a completely different reason for the break up (e.g. they
will lie and not admit they are breaking up because they found someone else). If they are particularly selfish, they will deny you had a relationship at all.
Steve: So I was just a victim of overlapping!
Joe: She did the same thing to me, why are you surprised? Every relationship of hers ends with overlapping.
Steve: But, I thought I was special.
Joe: Yeah, she makes everyone feel that way, until she flushes you down the
toilet, and moves onto the next best thing.