Sex File: I can't move on from her affair

"Unless a couple make a mutually agreed decision to open up their relationship, sleeping with someone else throws a hand grenade into any marriage, and people often react in strange ways."

Pic: iStock

After a bad patch in our marriage a few years ago (which I take responsibility for) my wife had a brief affair, which she confessed to me, and we have worked through in counselling. 

Although we love each other very much, and I trust her, I'm haunted by thoughts of her with her lover when we're in bed ourselves. How do I exorcise them?