Incest can be classified as sexual relations between two people classed as being too closely related to marry each other. When Arvi made love they were loverz and were enagaged to each other so that act cant be termed as 'incest'.
It might be classified as incest if arvi sleep together now but as far as we know they keep a dignified distance from each other and are honestly trying to move on in life. If arvi reunion will happen then i am pretty sure it will only be after arvi divorce their spouses. So, if arvi reunion does happen in the future then its not gonna be 'jeeju salli incest' like some people would like to believe. They cant even be said to be in 'jeeju salli relationship' for the fact that arvi are errr not in a romantic relationship. If they ever might be romantically involved in the future then its obviously gonna happen after they divorce their spouses. So no question of 'jeeju salli' relationship