I've lost a few friendships in the last few years. Just because they're comfortable and warm like those old slippers; doesn't mean they should last forever.
Sure it's over; but it still happened. They still kept my feet warm for a season. I can still be grateful for that.
Yeah you're right, nothing lasts forever, and sometimes the comfort or benefit of something having happened in the first place can go some way towards mitigating the ill-effects of the loss of it. Losing a pet is one such example.