For me, I actually don't mind being separated from anyone with whom I'm traveling (on a flight).

Unfortunately, for other passengers (when I'm traveling alone), I'll usually refuse to give up my seat if it gets in the way of one of two priorities for me:

A.) I need to have my overhead items (which are usually fairly compact) within arm's length from the aisle in which I'm sitting

B.) I need to be seated as close to the front of the plane as possible

Point A is necessary because I'm paranoid about another passenger accidentally (or deliberately) taking my overhead possessions once we land.

Point B is necessary for me only when I have a connecting flight to make. I intentionally always try to schedule my connecting flights with a fairly large layover time in-between connections. But sometimes those options are limited; or, even if I can get a 2-hour or 3-hour layover, I have no control over whether the first leg of my flight might get delayed due to unforeseen circumstances.

So, especially when I'm traveling on the first leg of two connecting flights, I'm highly unlikely to give up my seat just because friends/relatives who were traveling together got seated apart and want the convenience of chatting with each other throughout the flight.

If, however, I'm on the final leg of a connecting flight -- I'm more than happy to give up my seat so that family/friends can be seated together...as long as I can keep my overhead items within my line-of-vision.