The 3 are friends and she begins dating the second male lead thinking she likes him. She still tries to be close to the male lead, but he pushes her away thinking people might get the wrong idea. This makes her sad and helps her realize that she actually loves the male lead. 

Try:

Dal Ja's Spring 

Boys over Flowers 

Beautiful Gong Shim 

One more happy ending

My Fair Lady

Dalja's Spring

A love so beautiful

Summer Scent

My first first love is the first drama that came up to my mind.