He hung up the phone and stared at me.
Why would he just sit there and stare?
I think because he knew I was listening in on his conversation.
Getting stared at is creepy, and he shouldn't' do it, but you also shouldn't listen in on others' conversations. It's rude, and, well, gets people mad at you.
I wasn't sure if he knew I was listening or not. I'll never do it again but this is a red flag.
I think that you both should talk about this. I would let him know that it is rude to stare at someone like that.