Han terminado como el rosario de la aurora

[ROBINDESBOIS]

It means to finish very badly.
In English?:blackeye:

[poli]

To come to a bad end.

[JPablo]

Also, I though of some other possibilities (English natives, please, correct me if I am wrong)
To end in disaster,
or
To end in confusion.
Or
They wound up fighting.
They wound up in a complete rift.
They wound up badly quarreling and breaking up (like two lovers)
They wound up splitting up (in a very bad manner)