Sonic the Playa
Sonic the Hedgehog and Shania Twain... because I'm just that nutty.
Just how many girls can one teenaged hedgehog kiss?
Actual girlfriends
Amy Rose - Sonic X
Princess Sally - SatAM/Archie comic
Fiona Fox - Archie comic
Just friends
Julie-Su the echidna (Knuckles girlfriend/partner) - Archie comic
Sonia Hedgehog (sister) - Sonic Underground
Rouge the Bat games/Sonic X/Archie/others (See Scourge's love interests.)
Penelope Platypus - Archie comic (See Scourge's love interests.)
Could-have-been girlfriends
Mina Mongoose - Archie comic (they have other commitments)
Amy Rose - Fleetway comic (the only Amy who can take "no" for an answer)
Amy Rose - post-Sonic-Adventure games (she's not really a girlfriend yet)
Princess Elise - Sonic 06 (their relationship was erased from the timeline)
Shahra - Sonic and the Secret Rings
Blaze the Cat - Sonic Rush and later games; Archie comic
Flirts, flings and fan-girls
Bunnie Rabbot - Archie comic (when they were both lonely)
Nicole/NICOLE - Archie comic/SatAM (they exchange compliments from time to time)
Amy Rose - Pre-Sonic Adventure games (just a cute fan)
Amy Rose - Archie comic (wishes she was in Sonic X)
Breezie the robot - AoStH: "Lovesick Sonic" and "Sonic the Matchmaker"
Merna the Merhog - AoStH "The Little Merhog"
Roxy the Raccoon - AoStH: "Untouchable Sonic"
Miss Possum - AoStH: "Magnificent Sonic"
Sara - Sonic OVA
The hoards of fan-girls [insert face-palm]... - More than once Sonic has been literally surrounded by love-sick females, most notably in Archie.
Scourge's love interests - (Archie comic) Although he is a separate character (distinct from Sonic Prime) Scourge the Hedgehog is Sonic from another reality, so I'm including his girlfriends as "Sonic's love interests."...
Princess "Aly" Alicia (Evil Sally) - She walked out on him for being a poor leader.
Bunns (Evil Bunnie) - He cheated on her with Aly, Penelope and probably others.
(Evil) Penelope - never seen, only mentioned by Bunns.
(Evil) Nicole - He scratched their names into a heart once.
Most of Sonic Prime's love interests - He had some fun in Sonic's shoes one day.
Rouge the Bat - She ditched him when he started killing people.
Fiona Fox - He can't get enough of the good girl gone bad.
As always, I claim no copyrights. Most of the materials in this video belong to Sega, Sonic Team, DiC, TMS, Archie Comics, and/or Eggmont/Fleetway, samples of which I have collected from a wide variety of sources, including the videos of fellow YouTube users. Sorry, and thank you. Enjoy!