Santana from glee dating
Their first real on screen kiss was shown in the episode Heart (while they were dancing), after Santana dedicated Cherish/Cherish to Brittany (not counting the little peck in front of the locker shown earlier in the episode in a flashback).
Earlier in the episode, they had a near-miss: they were about to kiss, but Figgins addressed them ("Teen lesbians! In Saturday Night Glee-ver, Santana and Brittany are involved in a 'Sex Tape Scandal' because Brittany posted a sex tape of them on the internet (which displeases Santana: she was not consulted beforehand).
Schue says no to performing a number by Britney Spears.
They were considered to be best friends throughout Season One, until the episode Sectionals, when Brittany implied that they slept together (presumably more than once, as Brittany said that if sex was dating she and Santana would be dating), transitioning them to the "friends with benefits" status.
In season 2, Brittany dates Artie , leaving Santana lonely.
Santana becomes "beards" with David Karofsky (pretending to be each other's "significant other" to fool people about them being gay), to get Kurt back to Mc Kinley, win prom queen, and get Brittany.
Brittany responded with statements implying she was under the assumption they had been dating for a while.
During celibacy club, after Santana twirls in her skirt (while Quinn says "God bless the pervert that invented these skirts") if you look at Brittany you can see her bite her lip kind of sexily.
The two are often seen intimately cuddling, holding hands and walking with their pinkies locked.