Hey! The concept of broken bonds really interested me, so here is what I understand of it.
When a Kelvic bonds early, too early, before they are emotionally mature, and their personality fully manifests, it can harm them. It isn't the breaking of the bond that does this, it is the formation of a "light bond" as it can be referred as. A bond that can be easily broken, yes, and the Kelvic can move on with little trouble to form another, but they will continually form "light bonds" or bonds that do not have much impact on either of them.
Of course they are bonded, obviously, but not nearly in the same sense of the bonds formed later in life by the Kelvics that were not forced, or became, bonded to early. As said in the lore, they are protective, but not choosy in who they bond to.
This bonding is what hinders their development. They do not develop correctly, and can be mentally and emotionally confused or immature. Again, the lore states: "Their minds seem to freeze in a state of servitude that does not allow them to develop cognitive skills like a normal young adult would." Bonding again will not unfreeze this, it will be a forever hindered part of their mind. So, mentally, they have a development freeze. Physically, they will always grow and develop. They cannot just stop growing, and stay as a stunted cub or fledgling forever. They will grow, their minds just won't grow with them.
"In other words, a very young bonded Kelvic halts somewhat in their development and stays very simplistic if they bond too young. They also recover very well if their bondmates die or otherwise reject them. They can be bought and sold, and though their ties with their previous owners are severed, they can rebond easily to other owners."
Also, separation cannot break a bond. Now, the lore says "Bonds can be broken abruptly, especially the light bonds of a young Kelvic. If they are abused or neglected, often the bond will dissolve and free the Kelvic from emotional attachment." So, that might fall under neglect, in which a lightly bonded Kelvic might break / dissolve the bond. For deeply bonded Kelvics though, I do not believe separation would ever break the bond. One of the bondmates would have to break it, yes.
Hope this helps!
~ Lullaby