Rebound relationships are fuelled by a desperate attempt to escape the pain caused by loss.

"Smallness, dependence, separateness, feeling you have injured your good object, are all fairly obvious to the eye and not easily denied if one is facing reality. But reality is pretty painful much of the time in childhood, even when you have an intact family that is living harmoniously. Most children naturally gravitate to wishful ideas, the most fundamental of all being the idea that there is magic, and you can have it and instantly erase all of the pains I just outlined.

Every area of life that lends itself to the possibility that there might be magic will be seized for the use as magic. If I put on mom’s bra, it will magically give me breasts and I can feed myself. If I pick up daddy’s cordless drill, I will be able to do anything he can do, maybe even marry mom and be her husband."

Source here.

A rebound relationship is used as a magic charm to evade pain.