Why did Michael lie to Kay?

I'm curious to know, why did Michael decide to lie to Kay? Was there a particular motive behind his deception, or was it simply a spur-of-the-moment decision? Did he fear the consequences of telling the truth, or did he believe that the lie would somehow benefit him or protect him from something? It's intriguing to consider the reasoning behind his actions and whether or not he ultimately regretted his decision to mislead Kay. Did he come clean eventually, or did the lie continue to linger between them?