It goes by different names, but some people treat relationships like monkey bars, making sure they grab the next one before letting go of the last one.
That's also just like how soft-handoff works when changing cellular antennas while on the move.
That's what rebounds are for, and if you aren't up front about them being a rebound, you're an asshole.
But the healthiest thing to do is to be single between relationships. For a good long while. Until you're actually happy being single. That's the only headspace you can be in to find a partner who will be good for you.