(Need answers as soon as possible) Is my girlfriend playing with me?

I got into a relationship that is currently 5 months old. Everything was going well (dates were awesome, chemistry was there etc.) until last week where a huge quarrel started that is ongoing even till now. My girlfriend went for an orientation outing where she was game master for a station and after that, she had been messaging another guy whom she met. During the entirety of the relationship, other guys had messaged her but I never felt insecure as the messages were simply friendly and I felt no strange agenda in the messages. However, this one in particular felt strange. The messages were flirtatious like and although met only for a few days, they confided a lot in each other. Her behaviour also changed where she never hid her phone away from me but now she does. The past few days were also strange. Long story short, whatever actions we used to do together such as go to school together and go back home together stopped. I shared with her how uncomfortable I was with her messaging that guy and if she respected me and the relationship, she would stop immediately. However, she insists that he is just a friend and she also threatened to change our relationship status to single if I were to keep insisting on her to stop messaging. Also, right after her orientation event, she went to say that "we are breaking up for real" but yet she keeps blaming me during the past few days and says that i'm the one that wants the break up even though I had been telling her I want this relationship to work. She knows that I love her very much and i'm afraid that she is taking advantage of my emotions. Am I having my emotions being taken advantage of? Am I just overreacting to her messaging another guy? She kept on saying i'm simply overthinking and also insisted that I was the one who is strange because I only have problems with her messaging this guy and not the others. Any opinion is welcomed.
(Need answers as soon as possible) Is my girlfriend playing with me?
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