From a legal standpoint, parties can date after separation, or even before separation for that matter, and in most instances it will not affect your family law case.
If there are children involved, getting new partners involved in the children’s lives is not a good idea. Do not introduce new partners to the children. It will only cause problems in most instances, and it can affect the custody and parenting orders.
From a practical standpoint, nothing sets off a soon-to-be ex-spouse more than a new partner dating their soon-to-be former spouse. It can heighten emotions and make settlement more difficult.