This is a play on "female lead likes other guy before male lead". Are there any where the female lead likes the other guy, but has no chance with him. She then befriends the male lead and they fall for each other. Well then the other guy takes notice of her so she finally gets the chance she wanted. She breaks it off with the male lead to get with the other guy. The thing is when she begins to date the other guy, she's already too in love with the male lead so she breaks it off with the other guy and tries to get back with the main guy. They do. The End.

Seriously nothing?
I've never seen something like that, I just looked through my completed list and there's nothing that matches a description like that, which is kinda weird, because you'd think that would be something that would have been used liberally.
Very very close scenario:
Meteor Garden --- She falls for second guy, but he has a GF ...  lead guy likes her, she starts dating him, then second guy comes back and she leaves the lead to be w/ second guy ... then she realizes she loves lead guy, so breaks it off ... they go back and forth until she finally chooses lead guy.

Not exactly:
Summer's Desire  --- She is w/ first guy, they separate, she starts dating second guy ... first guy returns, they go back and forth ... until she makes decision towards the end .... But we don't know who she'll choose until the end..... She uses both guys!
Yeah Metoer Garden (Taiwan) is Boys Over Flowers (Korea)/Hana Yori Dango (Japan) so I've seen that. I liked the Korean version the best.

I didn't like Summer's Desire because the male lead changes midway through and I didn't like her ex.
Personal Taste it isn't exactly what you're saying but very much fits the format!
Suspicious Partner does the same but only in the beginning. 
@fiflydramalover

I've seen personal taste, but I'll check out Suspicious Partner.
My Fair Lady (Take Care of Agasshi) fits precisely.

That Fool (Accidental Couple) also fits.
@ManfredvonRichthofen

I'll check out My Fair Lady.

I've seen That Fool which is really good. Though the end doesn't really fit because she never gets back together with the other guy.
Any more that fits the scenario I listed above?
Hmmm, maybe General and I. She falls for the main male lead, leaves him for the other guy, then goes back to the main lead. It happens early on though and is more of a set-up for the plot than the entire plot itself. And she does't really like the other guy, he's more a brother she's sworn to protect. 

Marriage, Not Dating kinda sorta fits? The leads are both 'using' each other (i.e. fake relationship), she gets with the second lead while in the fake relationship with the main male lead, but falls for the main guy.