If it is only the headband and/or tailband (
Picture) that's going loose, and not the binding itself, you can fix it with regular glue you can use for paper (the white one you can use for paper and cardboard). If it is only the headband or the tailband, the binding should be totally fine and will not break.
I had the headband and the tailband loose and used this:
Uhu Bastelkleber (Sorry, i did not find a english equivalent).
It is important, that the basis of the glue is wood glue (normally just thinned with water), otherwise it's too stick and will break.
(I just found out that there are no english words for Basteln and Bastelleim / Bastelkleber. Can anyone help with that?).
BUT: If you have the feeling that the actual binding (the white rubber-like thing which has contact to the pages) is broken, you should contact Evil Hat.