The A was exposed or you came clean to your BH? I thought you'd owned it. Have you stopped all contact with OP? Have you changed your numbers, emails, etc? Does OP leave in your neighborhood, where you could bump into each other? Did you write an NC letter to OP, with your BH's approval and send it together?
For a 14-month affair, I would imagine you will experience withdrawal for about three months...long road. You'll know when you're coming out of it when you stop going into the future (like fearing your BH, not your S...he was that before you chose an A) will never be good enough. Woman up, LITW...you are choosing not to see it now, but this is the man who you were in love with, chose to marry and vow to...not your old flame who crashed and burned once already...your BH is doing the job and has the status. You can crave BH again, body, mind and soul again...up to you to do your personal and marital recovery.
Would you consider that it's difficult for you to stay away from OP because it's really difficult for you to stay away from fantasy? Easy for you to create and build resentment in yourself (from thinking in the past and the future, neither of which are real)?
See where your urges come from in you. You choose to love, act from it...there's no magic. All you...getting really honest with yourself, making it your highest priority and owning it's you, not him, which finds others attractive.
What are you reading to aid your counseling? How many hours of UA are you guys spending? Have you answered all of your BH's questions about the A honestly, to the bone? What exercises did your MC give you to do together?
What do you mean you are both in Plan A now?
Have you read Surviving An Affair by Dr Harley?
Do you still believe your BH could cause your A?
All of your emotions come from your beliefs...know what you believe, if they are valid from your adult experience...and if they are healthy.
What else are you doing to honor your marriage right now?
LA