Hi, I'm in the same boat as you and LWB (H still in contact with OW). Does H know that you now know he is still seeing OW? If it were me I would let him know. That happened to me, I found out H was intimate with OW after d-day and I called him out on it. Told him if he wanted to do that and be intimate with me, he could leave. I would not stand for that disrespect.
I'm with LWB about if you should tell him you're going dark. I'm not sure. On one hand, it would help set boundaries. Perhaps letting him know that you're no longer going to let him have his cake and eat it, too would knock a bit of reality into his fantasy world. Going dark gives them a taste of what D would be like. And gives you a chance to distance yourself from the exhausting emotions.
