I imagine the wife would file for divorce on the grounds of his adultery, the person who he commits adultery with does not have to be named in the divorce petition. A divorce petition can be issued even if they are still currently lving in the same house (but separately). Alternatively, the wife could issue a Petition on the grounds of unreasonable behaviour and irretrievable breakdown of the marriage.
Alternatively the parties have to be separated for two years and both consent to the divorce or be separated for five years without consent.
Arrangements for children of the family under the age of 18 are taken into consideration at the outset of divorce proceedings