Whichever one realizes the relationship is doomed.
When a romantic relationship is doomed to fail and the attachment cord should be severed ...is it better to be the cutter or the cutee?
I don't there is such a thing as a 'better' position to be in a romantic failure. No one wins .. It's not a competition. Both parties must deal with thier own colateral damage in one way or another .. And move on.
As the song goes:
There ain't no good guy; there ain't no bad guy; there's only you and me and we just disagree."