If you truly realized and knew your worth, this fox would have not been able to get into the hen house. You were so consumed by your need for validation and love that you chose to put the needs of someone else, i.e. sex, above your own needs. And honestly, you played yourself and allowed yourself to be played!
Have a discussion with them about how you feel, how the friendship is taking a toll on you and how the friendship is affecting you negatively.