What is the concept of Fiancé/Fiancée in Islam ?
I come from a pakistani background and I know many people who get engaged for 2/3 years and its acceptable in the culture too. But what does Islam say ?
Engagement is a mere promise for getting married. It is allowed and it is sunnah. A man should not propose to a girl who is already engaged. See the following hadith that is graded sahih;
The Messenger of Allah said: "A man is not to sell over his brother's sale, nor is he to propose to whom his brother has proposed." (reference)
Engagement is reversable, man or woman can change his/her mind regarding their promise.
On the other hand, it should be noted that engagement doesn't make lawful unlawful and unlawful lawful. Until the marriage, men and women are considered strangers and should be treated as strangers regarding male/female relationships.