Most Helpful Girl
It's awful, but it depends on why. If her feelings have simply gone it's more of a relief that it's over and you can move on, although hurting someone will never feel good.
Breaking up with someone you're still crazy about, but your relationship isn't healthy and/or you're hurting each other and it's just something that's for the best, it's the worst kind of pain.
Its not dissimilar to grief. You get home, and everything seems quieter and emptier. You're a bit lost for a while.
... but again, there is still that slight relief.
Hurting someone is never nice. I've lost sleep over guilt about the way I've treated a guy before.
It sounds silly, but if you've ever seen 9 1/2 weeks, the ending isn't that sad to some people, but to any woman who's reluctantly left a relationship, it's one of the realest, most relatable endings. We've all done that walk and/or we've all felt like that.
Most Helpful Guy
The reason you're hurting and she's not is that she was already over the relationship when she dumped you. You're not over the relationship yet.
And being the dumper usually sucks, unless you're just so sick of the other person you're happy to be rid of them.