Could that be when Buffy figured out that Willow was in love with Tara, in “A New Moon” from season 4?
No. I’ll give you a hint. It was from Season 5.
I’m still only on season 4. 
In a spoiler, since one poster mentioend only being on season 4
The only thing I can think of is Glory to Buffy/herself/everyoen when she finds out she was fighting Buffy-bot and is about to get smacked with a Troll hammer.
It’s from earlier in the season. The quote is in reference to Glory though.
It’s Buffy to Quentin Travers, after he reveals that Glory’s a god.
“And Eve, for some reason.”
Angel to everyone else when he was recalling all the stuf from his demon induced nightmares.
Incorrect.
Angel to Cordy re: remembering Connor in You’re Welcome
and to return in kind:
“or Spike, for some reason.”
The quote comes the Lovers Walk ep. Buffy is talking to Angel about how they aren’t friends and can never be friends. She can fool herself but she can’t fool Spike “for some reason.”
My quote is “I left reasonable about 3 exits back.”
Riley to Spike, in Into the Woods
“Well, see, I like that you’re unpredictable.”
Oz is talking to Willow about how he is going to ask her for a date, but not right now. The ep is Surprise
My quote is " Well, that was pathetic."
Spike to Buffy about her conversation with Parker in Harsh Light of Day
I’m not actually sure that’s right, so here’s my tenative quote:
“Ooh, aren’t we just the scary serial vamps - with the spooky lair -and the taking of trophies of our victims? Lame. Next time you hit the yard sales, I’d avoid the wooden furniture. I hear Wicker is nice.”
you’re correct on all particulars. Are we the only 2 left interested in this game? Do you think, if we are, its worth continuing? Let me know.
An Angel soliliquy during “Provider” when he’s hired with a fake check to clear out a nest of vamps, and demons decide Fred’s brain is just what they need.
Miles to go… Little Ms. Muffet counting down from 7-3-0.
Dream-Faith to Dream-Buffy in Graduation Day pt 2.
“It’s against all laws of God and Man!”
Willow to Xander in “Innocence.” About Cordy.
“Endless committees were formed. Committees splintered into factions, the factions into coalitions, the coalitions turned into subcommittees, until finally the more radical element, spurred by a charismatic leader, did the dance of revolution.” 
Groosulug to Cordy, in Couplet.
“Why didn’t you just go to Muu Muus R Us?”
Buffy to Joyce in Bad Eggs
“I love you like pancakes, but I’m gettin’ the hell out of here”
That’s Fred to her dad or mom in the opening flashback in “A hole in the world”. I believe a piece of my soul died the first time I saw this ep. And I wasn’t even a regular watcher at the time.
“Thank you. I’m…very comforted.”