If there is risk of false cases (forgery/rape) during livein relationship, there is also risk of false cases (498a, DV) in marital relationship. By the way, 498a can also be filed by a girl during livein relationship (there are SC citations).
At any rate, the questioner wants to know if it is illegal to live with another girl during pendency of divorce proceedings. Though several experts have posted their opinions, it is not clear if it is or if it is not. Some are saying it is illegal and others are saying it isn't but there are risks.
As far as my limited knowledge goes, it is not illegal to live with another girl during divorce proceedings if that girl is not married.