jealousy hit me eight months in, not at the start

Married ten years, doing this for roughly eight months now, and until about three weeks ago I would have said it was the best thing we’d ever done for the marriage.

The first six months were genuinely easy. She’d go out, I’d feel that mix of nerves and something better, she’d come home and we’d talk half the night. I kept waiting for the jealousy everyone warned me about and it never turned up. I even got a bit smug about it, told myself I must be wired differently.

Then a fortnight ago she was out with someone she’s seen a few times before, nothing new, nothing that broke any of our agreements, and I sat in the kitchen and felt genuinely sick. Not the good nervous. The other thing. It lasted about two hours and then went, and it’s come back twice since.

She knows, because I couldn’t hide it. She has been decent about it and has offered to pause everything, which I don’t think I want, but I also can’t explain why I don’t want it.

So the question is really: is late jealousy a thing? Did it arrive months in for anyone else, and does it mean something different than the early kind?