Confront your husband. Tell him you know what's going on and it has to stop now. If you have children, make sure to let him know that his actions are destroying his family and he needs to stop his nonsense.
Step2
Tell him he needs to let that hussy know to back off and leave your family alone. He must sever his ties with her for the good of your family.
Step3
Go to counseling. You'll both work through it and be a lot happier in the end.
Step4
Don't keep him on a short leash. Sometimes if a husband does something stupid like this, the wife will have a tendency to "keep him on a short leash." This can typically have an opposite effect from what you're trying to achieve.
Step5
Keep communication open. When communication stops, the relationship will die.
Tips & Warnings
communicate with each other
don't keep him on a short leash (but don't let him just run around either. Find the happy medium)
Enthusiast 
