Do affairs at work happen straight away or over time?

I've seen some messages beyween my husband and one of his employeees (she very pretty and around the same age of 33, plus she's also married)

Nothing massively untoward has been said but they are VERY comfortable with each other with some minor constant flirting going on.

They have worked together for like 2 years so if an affaird was on the cards, would it have happened already? Or should i still be slightly worried? He doesn't talk to anyone else in the same way as her.

Do affairs at work happen straight away or over time?
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