What does it mean when a guy gets embarrassed like this in front of a girl?

One of my guy friends got really embarrassed around me last night. He and all his fraternity brothers were with a bunch of girls and happened to be at the same restaurant as me and my sorority sisters who were there for a birthday dinner

He came up to me and seemed pretty drunk. I became friends with him in the dorms last year and there was a whole group of us who were close. He started asking me how I was/been doing and talking to me and then he asked me how my friend "Jess" was. I told me him she was good and then I made a joke "yeah you loooveeee Jess!!" because him and jess slept together a few months ago and he didn't know that I knew so I was giving him a hard time and he realized I knew. Well jess used to be one of my best friends and was part of the "group" from the dorms. She was/is super ummmm "loose" I guess you could say and I'm the complete opposite (still a virgin).

Well he got all embarrassed and was like "You know I"m not like that Christy, right?" "That was just a really weird night!!" and he kept trying to convinve me he's "not like that" and that is was just a "weird night" and I kept giving him a little bit of a hard time like teasing him and he just kept getting embarrassed trying to convince me it was nothing. He eventually walked away because he was getting super embarrassed and felt awkward or something lol. My other guy friend who is his best friend and was there too was like "Yeah good job Christy!!" and knuckle pounded me for it hahahahah and then was like "I'm sorry he had to make that so awkward!!"

Why did he get sooooo embarrassed? He seemed like he was ashamed that I knew about it and I don't get why he would care so much
What does it mean when a guy gets embarrassed like this in front of a girl?
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