Alzack & Bisca:
They got married during the 7 year time skip. They also have a daughter called Asuka.
Scorpio & Sagittarius:
They've been dating since the start of the series.
**Complicated**
Levy & Gajeel:
It is evident in both the manga and anime that they like each other, however they are too shy to admit.
Erza & Jellal:
It is evident that they both like each other. They kissed in the manga. Jellal thinks he's not good enough for Erza, so he lies and tells her that he has a fiance. Erza is aware of this and calls him a "bad liar".
Evergreen & Elfman:
These two obviously like each other. It is hinted many times in both anime and manga. They're too tsundere to admit it.
Happy & Carla/Charles
LOL. I have no idea why these two...