Khadija's Proposal to the Prophet Muhammad

An elderly lady by the name of Nafisa it is said that she expressed an interest in marrying the Prophet. Khadija was the one who instigated it and hinted at it or kind of sort of arranged for the Prophet to propose. The details differ about how the proposal came about but they all agree about one thing. Falling in love is a natural emotion, it's nothing wrong with that at all. Even in Islam if this happens with certain guidelines then of course this is completely permissible.