Questions: Dating

We both know a guy from work. Two weeks ago we ask him to take his bike for a ride but he said sorry no. After that day I see him everywhere I go at work he is kind when he talks to me. I don’t know much about him but he seems as good guy whatever yesterday we saw that guy outside and my boyfriend was making jokes about beating him and I said stop it he is a good boy. He changed his face and asked how do you know that? He is a good guy huh? We talked little bit about him. I told that we talked the other day and he fixed his bike and he was like he told you that? He didn’t tell me anything. When we finish talking about that guy my boyfriend started asking about other guys like do you know him? Is he a good guy huh? And I was surprised because he told me he’s not jealous but now he was being. I said babe I was just kidding I didn’t even know about that guy until we ask for his bike. He laughed and said yeah I’m joking too but he kept asking about himself like do you know me? I’m great and I replied him oh my god yes you’re perfect and the best. Later on the day we were texting and I don't know how many times he used ‘good’ he was texting you’re good girl etc…I texted him ‘didn’t think you’d resent this much about that guy lol’ he texted me back ‘lol I just found it funny’. Why he is acting like that?