I don't think I understood the whole thing about people yearning for their exes until I had my most recent ex.
My first ex I went totally off after we broke up, and while he's a nice enough guy who I could be friends with, in theory - if stuff wasn't so awkward as I can see he now is with me - I no longer saw what I used to see in him. Any appeal evaporated so quickly with how sour it all went and then the many faults as a partner were glaring.
My second ex things got left better with, still kinda friends but more occasional ones than as close as we once were. Going from effectively best friends to much less than that has always been the most painful part of a breakup for me. I think even though we broke up, we both came out of the relationship better for it. I can see our growth and it makes me pleased for who we both became after. I know we're both in a better place now, she seems happier (and both polyam now, lol what a surprise after we used to talk crushes together) and that's just really nice to realize.
But my latest ex, it's been well over a year and a half and it still hurts and makes me wish things were different. I know we're incompatible on several levels (me polyam and him not being entirely okay with it, me only wanting to adopt, if that, and him possibly wanting his own kids + not with me if I'm still polyam, different attitudes on sex and sex drives). I know we made each other unhappy probably as much as we made each other happy, kinda cancelling it all out, but sometimes I still just wish we could be together. We remained very good friends but didn't get enough distance probably for it to count as properly separating and so distance now due to the pandemic is extra painful but possibly overdue. I just wanna turn the caring off but I don't know how to. I thought after a year or more it would be easier but it isn't.
I also keep wondering about joining an ace dating site but during a pandemic seems a bad time to try that? Also dating as demiromantic (or maybe greyromantic? Something not quite how people expect re romance) is extra hard unless people are gonna be okay with maybe finding new friends as the alternative if that angle never develops. So I guess I'm a bit scared to try again and not sure if it's worth it when I do have one partner still. No clue what percentage of ace people are okay with polyam either. But I think I would like more love in my life in some way, whether that's romantic or queerplatonic. It would be nice to actually find friends and/or partners to be domestic with because I love sharing that kind of caring with people and I think maybe that's what's been lacking for me.