Why would this guy act like this if he has boyfriend?

My guy friend goes to university that I'm attending. He introduced me to he's 3 friends and one of them since we met acts differently torwards me than other boys. He wanted me to hang with them. I've noticed he stare and smile at me a lot and if I would ignore him he would become mean. He was really sweet torwards me and always wanted to help me. At first we didn't talk, it was pretty awkward between us, but after some time he would come really close to me. He was always around me and teased me all the time. Even my guy friend thinked that this guy liked me.

After some time, me and that guy started to send text to each other in private box and he said to me that him and this other friend are in relationship (they are moving together next week). I ignore him since that text. I was so confused, he acted like that infront of his boyfriend... He's boyfriend was always nice to me but never like this guy.. no guy ever looked at me like that... he always stared at my eyes I really felt connected to him.

Why would he acted like he likes me if he has boyfriend ( I'm girl by the way)?
He wanted to boost his ego
Vote A
He likes you more than his boyfriend
Vote B
Other (comment)
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1 y
He was always quiet and awkward if we would be alone together.. and he would become really nervous if he needed to sit across me.

After my guy friend said like 'he's such a great friend to you' to me, he become really distant and cold torwards me for like 10 days now.
Why would this guy act like this if he has boyfriend?
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