Bad idea, because he might find out and get cranky about it. But maybe you could just grab a syringe and extract some spinal fluid from his spine so he can’t walk. I suppose then you could tell him you’re seeing someone else. If he can’t walk, he’s less likely to discover it’s all a fib.
I’m thinking, you should also cut off his fingers so he can’t text you about how miserable his life’s become.