i'm 10 months out and they still happen to me on occasion. You are not alone here!!
The OW lives down the street from me. So i see her car, house...HER. all. the. time.
your WH works with OW. You may not see her, but your WH does.....the proximity is there.
When you feel it coming on...face it head on. Talk to your WH. Ask for reassurance. Call him at work just to say "hi". Make plans to meet him for lunch. Chat or text him. Tell him you are feeling down and why and get the boost you need to feel reassured.
Another thing i did was to have my WH text me a picture. When i started feeling wonkey I'd text him "need a pix". he'd have 60 seconds to stop what he was doing and text me a pix back. Didn't matter if he was in a meeting, at lunch with co-workers, whatever.....he stopped what he was doing and sent the pix.
hugs to you!!