Rainbow Dash is not gay. Shocking, I know.
However, Bonbon and Lyra are.
Octavia and Vinyl are, if not lovers, very close friends.
Fluttershy and Big Macintosh are quietly dating.
Twilight Sparkle will eventually achieve alicorn status. She is effectively immortal, the magic suffusing her body preventing lethal harm.
On the topic of Alicorns: They are immensely powerful creatures combining unicorn magic, pegasus flight, and general earth pony toughness. They are extremely long-lived, but can be killed. They draw power from what they represent: for example, Celestia draws her power from the sun. While their element is active, they are more powerful. Thus, Luna would be more powerful at night.
Ditzy Doo, nicknamed Derpy by the local ponies, is not as dumb as she makes out. (These conclusions are based off of
The Pony Psychology fanfic, one of my favorites.) She was originally in the CIA (Celestia Intelligence Agency), working undercover for the mob. She sustained brain damage in a fight against the griffon mob boss when she broke his beak with repeated headbutts. Now that she's recovered her memories and finished the job, she acts slightly disabled in order to protect her two daughters, Sparkle and Dinky, from the mob.
Doctor Whooves exists, is a Timelord, and has settled down with Ditzy.