Edna Krabappel
In "Grade School Confidential", her relationship with Skinner almost made them married. However, in "My Big Fat Geek Wedding", Skinner does not want to marry Edna. This made Edna sad and their relationship became unstable. In "The Seemingly Never-Ending Story", it is shown that she liked Moe Szyslak before she was a teacher. When she first met Bart Simpson, Moe stopped the relationship.