What are the limits of interaction which a boy and a girl must observe before entering into a wedlock? Is falling in love a sin?
Before I answer your questions, there is one thing which I would like to state as a principle. The Sharī‘ah revealed by the Almighty is very brief. A lot has been left to human intellect to tackle. Only in matters, in which human intellect is liable to falter, does the Sharī‘ah gives guidance.
According to the Sharī‘ah, men and women coming in social contact with one another should observe two regulations: they should guard their gazes from taking undue liberty and take care that the dress they are wearing properly covers them. Women should observe three additional regulations as well: firstly, they should cover their chests by their head-coverings; secondly, they should not display their jewellery except that which is evident, (that is jewellery worn on the face and hands), and thirdly, they should not strike their feet in a manner which draws attention to any ornaments they may be wearing. Consequently, men and women while observing these regulations can eat and converse together1.
This is all as far as the Sharī‘ah in this regard is concerned. Keeping in view these directives and the norms and traditions of an Islamic society, which themselves need to be followed as per the dictates of the Sharī‘ah, a boy and girl can meet each other.
Among these norms, perhaps the most important one is that all activities that can damage the reputation of a Muslim lady should be avoided. The most important thing in this regard is that a boy and a girl should never meet alone. They should meet in the presence of elders.
Falling in love is no sin. It is but natural. Islam does not object to it so long as the boy and the girl do not indulge in things that tarnish the mirror of their souls – for purification of the soul is the real objective of Islam. Believing men and women must always keep this in consideration. In this regard, the Sharī‘ah pertaining to social interaction described above as well as the norms and customs of a society must also always be taken in consideration.
If circumstances are conducive, the boy and the girl should try to marry one another whenever suitable keeping in view the norms and traditions of the society they live in.
1. See the Qur’ān (24:31).