Leviosa
I think of a rebound in a somewhat different way than what I think you mean. I think maybe, though, that it could be sort of the same thing. Kind of a Ms. Right vs a Mz Right-Now. This person might just see you as someone near that's a sure thing to fill the gap left by someone else. They know how hard you tried to make it work so they think you're the most likely person they can fill that gap with without going through the process they'd have to go through with someone now.
This doesn't sound like a far fetched possibility. I suppose this is a matter where only time will tell. Thank you for your ideas Grizabella.