Here's what I got from your description of his actions;

He's started seeing someone else. You're not in an exclusive relationship so I wouldn't expect him to he honest about whether or not he's banging her too, especially since it probably means he would stop being able to bang you, and you're letting him raw dog it. Why would he wanna lose that?

So either way he's not going to tell you he's banging someone on the side. But I can promise you he is because you aren't committed to each other. So for your physical and mental health, I'd cut the sex off until he can make a decision.

He expressed some defensiveness and secrecy with his text and when you asked a simple question of who was that? He started saying he feels cornered. How did you corner him? You waited a while then simply asked in text. His reaction is a red flag.