Why would he question me about if I am giving it away to someone else?

My male lover has been calling me but I have not been responding to his calls.
So one day he calls me I am at work I didn't answer so he called right after that.
He then text again ok lol.

So few days I do reply back and told him I was busy. He had the nerve to ask if I am having sex with one else. I don't give him an answer so he goes are you giving it away. Because I did't answer the question we can't get on with conversation because he said you didn't answer my question 3 text ago.
What was the big deal we are not a couple so why would he be wondering if I am with someone else. Guess he hasn't heard from me so he figured.