Silsila (1981)

Although orphaned at very young ages, Scriptwriter Amit and military pilot Shekhar are brothers and also very good friends. The latter is happily engaged to Shobha, while the former has just fallen in love with pretty, young Chandni. But tragedy strikes when Shekhar's plane is shot down in Kashmir. Amit feels it to be his obligation to leave the girl he loves and marry his brother's pregnant fiancée instead. But when, by an unexpected turn, Amit and the now also married Chandni meet again, their love for each other proves to be stronger than their marital vows.