Your boyfriend promises to marry you on different conditions: when he finds a stable job, when he saves enough money for the wedding, when he gets 28, or when he's tired of being single. Whatever it is, you patiently wait for that day to come. Then one day he said he changes his mind. He's marrying you no more.
Can you sue your fiancé for his breach of promise to marry?
Of course, yes.
But another question would be, can you compel your fiancé to pay you for his breach of promise to marry? In legal parlance, is breach of promise to marry an actionable wrong?