I absolutely believe that continuing the friendship is just an invitation for future trouble. Let the friendship drift out of contact the way she generally ceases to contact you when she's in a relationship.

Perna suggested great, practical advice however. The idea of being couple friends is great, IMHO, but then again, you can make other friends as a couple as well.

Your wife may not ask you to set limits on who you are with largely out of respect for you. However, perhaps YOU need to set your own limits on who you share your time with out of respect for your wife.