Okay, so I read this oneshot once about a girl who started dating this guy right after he broke up, saying she would be his recovery girlfriend until he was over his ex. The problem is that I can't remember what it was called. It might have been attached to another manga as well, I honestly just can't remember. Please help!!

Sounds like the extra story in Gold Rush 21

yeah,asahina's right.
it's called Love Started.