I Only Have Eyes for You by The Flamingos is featured in Sadie Hawkins, the eleventh episode of Season Four. It is sung by Ryder with Artie, Joe, and Unique singing backup.
When Brody asks Rachel to dance after he arrived late to their date, Rachel objects that there isn't any music they could dance to, to which Brody tells her to imagine the music. Then the song starts.
Back in Lima, Ryder watches Jake and Marley, dancing, with a sad expression as he sings. Jake and Marley both dance and kiss later on. Blaine returns to Tina, saying he couldn't miss the last dance with her. We can see Becky and her boyfriend too, as he leans down for a kiss on the cheek.
As the song comes to an end, Brody announces that he wants to move closer to Rachel. Rachel suggests that Brody moves in with herself and Kurt instead.
Ryder (with Artie, Joe, and Unique):
My love must be a kind of blind love
I can't see anyone but you
Are the stars out tonight?
I don't know if it's cloudy or bright
(I only have eyes for you, dear)
The moon maybe high
But I can't see a thing in the sky
(I only have eyes for you)
I don't know if we're in a garden
Or on a crowded avenue
You are here
So am I maybe millions of people go by
But they (All disappear from view)
And I (only have eyes) (Artie, Joe, and Unique: Only have eyes)
I only have eyes for you