Belle was the love interest of Ebenezer Scrooge in A Christmas Carol and every adaption. When she was engaged to him, he kept pushing the wedding back until his finances were no longer poor. After seeing that he ultimately cared more for money than for her, Belle eventually broke off their engagement.
In some versions, including the original, the Ghost Christmas of Past showed Scrooge how Belle eventually found true happiness with another man--they fell in love, got married and even had a large family together. Seeing this caused Scrooge to further withdraw from society and relationships.
The Ghost of Christmas Past reminded Ebenezer Scrooge of when they met and when they broke up.