My bride (40 years) and I prefer to sit together on the rare occasions that we fly together, but it's not a deal breaker. I just don't understand the big stink being raised by the OP. Yes, it's disappointing. Maybe most of the others wouldn't trade seats because THEY were traveling with someone and wanted to stay together. Could be spouses, could be business partners on a working flight. Their reasons are their reasons. The F/A took that seat for a legitimate reason.

Something like this could also happen in coach. The rear jumpseat could be broken and a pax on the aisle in the last row could be displaced. Or, you could have a seat in a front row of coach and get bumped by a wheelchair pax. That's happened to me a couple of times. Things happen. We still all get to our destination at the same time.