Have two Star Wars droids ever been in a relationship together, either in-canon, questionable canon or not-canon?
R2-D2 and KT-10 (Star Wars: Droids)
C-3PO and LE-914/Ellie is a possibility - he cried when she died (Star Wars #80)
Bonus round: Organic meatbags vs. Droids:
- C8-42-GE3 was the object of romantic affection of Elise Montagne. No, this was NOT a fanfic - it happens in Knights of the Old Republic.
You can read all about these, and other weird romantic relationships in TGFFA (Luke and Leia nonwithstanding), in
fanfiction.net starwars.com blog article "I’d Just as Soon Kiss a Wookiee: Star Wars Romances"