^ Uhm, yes that can happen. Technically, it's not "falling in love"... having affection for a sibling is natural as you have that familiarity, but some people who are "mentally unstable" take that "affection" too far and misconstrue it as "love", and thus it becomes incest. Those guilty of it can be prosecuted as it is illegal in most countries.
Why, have you fallen in love with a sibling? I think that must be the last thing that has not been discussed in Life1.
I dont think someone fell in love with sibling, but rather the fiancee of his sibling. For example 2 brothers and the elder got engaged to girl X. The younger brother falls in love his future babhi, and in some cases they even run away together. So sad. Any babhi should be seen as a sister for guys and that's it.