Why did Michael lie to Kay at the end?

I'm curious to understand the motivations behind Michael's actions. Why did he choose to deceive Kay at the end? Was it a spur-of-the-moment decision, or had he been planning it all along? Was there a specific reason why he felt the need to lie, or was it simply a way to avoid a difficult conversation? I'm eager to gain insight into the intricacies of his character and the factors that influenced his decision-making process.