Montesquieu

“Marriages among the Germans are severe,” says Tacitus ; “vices are not a sub­ject of ridi­cule to them1 ; to cor­rupt or be cor­rup­ted are not consi­de­red a cus­tom or a man­ner of living ; "there are few exam­ples in such a popu­lous nation of the vio­la­tion of conju­gal troth.”2

That explains the expul­sion of Childeric : he affron­ted rigid ways which the conquest had not had time to change.

[…] severa matrimonia […]. Nemo [enim] illic vitia ridet, nec corrumpere et currumpi sæculum vocatur (De moribus Germanorum [ch. xviii-xix]).

Paucissima in tam numerosa gente adulteria (ibid.).