The principle of no-fault divorce is established under in Family Law Act. This means that a court does not consider which partner was “at fault” in the marriage breakdown. While it is a highly emotional issue, the cheating is not a legal issue. The fact that your partner cheated does not give you any advantage when it comes to property settlement or child support or custody.
The only ground for divorce is the “irretrievable breakdown of the relationship”, demonstrated by being separated for 12 months.
If there was an issue of family violence, then that would affect child custody arrangements, but that is a separate issue from the infidelity.