Sitting together

Ashkenazi practice is that, when the wife is in niddah, a couple may not sit together on a seat where the movement of one person can be felt by the other. This could apply to sitting together on a couch. But it is not the case for a sturdy sectional couch if they are on different sections. Therefore, a couple may sit on the same couch if it is sectional, or has separate pillows along the seating surface, as long as they are not sitting close enough to touch.  They may also sit next to each other on a sturdy, hard bench or other such immovable surface.

Whether or not sitting together on a sectional or sturdy couch is appropriate may also depend on the circumstances.  If they are with a group of people, sitting together is less of a problem. In a more intimate setting, the couple should use common sense.

Nowadays, the laws of tum'ah no longer have practical applications.  There is not usually any reason for a husband to hesitate about sitting down at a place his wife has vacated.