I would nip it in the bud pronto , my husband of 24 years walked out 7 months ago on me and our children I found it recently it was all down to a secret coke habit , he’s lost his car his savings his family his own self respect , confront her in a non judgemental way but make sure you face up to it right away the heart ache and devastation my husband has left is heartbreaking ???? good luck