User blog comment:Crazylittlefreakgirl/Fairy Tail Official Pairings?/@comment-24.212.145.235-20131225154632/@comment-7418318-20131225182137

They aren't in relationships with other people, they aren't from different social standings (well... not anymore), nobility or countries, they aren't parts of hostile families, they aren't from competing guilds, they aren't related and they are very close to the same age.

So I really don't see what "forbidden aspect" you are talking about.