Embaring situation, she tries to flirt with me right in front of her husband. What to do?

I had that situation for about 5 years, every time I was out with a certain couple. One evening after some drinks the woman actually told her husband in front of me that if he died she would marry me. Talk about uncomfortable. A few outings later and he finally said something to her and it hasn't happened again. I notice I rarely hear from them now though. Her flirting cost us all a good friendship.