@mathprofbrony  
Implying Stinger is the follower.  
Nevertheless, they are tied by destiny.
 
Vapor is the only one for Sky, and Sky is the only one for Vapor.

@SeraphimDawn
 
Well, notice Vapor Trail already had her cutie mark when they met; Stinger didn’t.

They were destined it seems.

As I just posted on a different image a moment ago, one way you might interpret these two is that Vapor Trail’s star (which she got first) is what Sky Stinger’s cutie mark is depicting, seen from the viewpoint of a pony following as it vanishes into the distance.
 
This sort of cutie mark is unfortunate in some of its implications but perhaps the kind of thing one is subject to if one is insufficiently independent when cutie mark time hits; like any cutie mark, though, there are optimistic interpretations, one of which Sky Stinger presumably latched on to without suspecting a “follower” interpretation.