platonic friendships

A friend just shared with me that her husband has a good best friend who is a lady. And she ,as the wife, is not jealous at all of the friendship. Her husband and friend have known each other since undergraduate days. They still keep in touch even after he got married.It is so refreshing to hear that true platonic frienships can exist and why not, one may ask. Surely, two matured individuals of the opposite sex can learn much from each other , through their sincere and genuine frienships, married or not. Does a good friendship between the opposite sex allow to exist only within marriage?
Of course, there must be boundaries , even in a platonic friendship. Maybe the common interest and attraction is only in the area of the mind and nothing physical.
If you are in a platonic friendship now, value it and let it nurture you in your life's journey.