Why was he texting another girl in front of me?

I have a crush on a co-worker. We've been flirting for about a month now and even yesterday he was always touching my leg and when I was texting a friend and he got all jealous asking me who it was and stood next to me to read the conversation. And it's not even the first time he acted that way. And today, we were talking and he said "Wait, I'm just sending a message to a lady". Why? Ok, he can text another girl, we're not even seeing each other but why did he have to tell me? When he texts his friends he doesn't tell me he's texting one of his friends. Why did he have to tell me he was texting a girl?
Yesterday he went to a party that I was supposed to go too with my friends. Initially I said I wasn't going but then changed my mind and texted him saying I changed my mind because he had asked me to go. ( He knew my friends would be there so I didn't necessarily need to go with him but he still wanted me to be there). And he only saw my text this morning even though he was online several times. The way he reacted this morning when he saw me I could see he was trying to see if I was mad. I acted normal because I don't want him to think I get mad over petty things.
I'm not the best at expressing my feelings and even if I'm trying my best to show him I'm interested, I admit he might have a little bit of trouble picking up my signs. Was he trying to see my reaction to him texting another girl or was he trying to show me he's not interested in me?
Why was he texting another girl in front of me?
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