Why does my girlfriend talk with all these guys?

like i started dating this girl right i love her and she loves me back (according to her), but when we are at school i see her talking with other guys and sometimes she just holds my hand and like ignores me while she is talking to this guy. Theres this guy who also got on my nerves cause she talks to him like more than she talks to me she like talks to him only after 6th period and in 6th period (i have the same class with her). and one day they were cracking up and i told her like smiling what happen and she was like oh nothing and im like (in my head) wtf. and another day i saw her at that guys desk and she was bending over his desk that day i got so pissed even the people in my class were like oh you broke up with her already and im like no! So yeah i mean this is kinda getting to far and when sometimes when shes talking to me by the phone she starts texting her cousins and friends (im not sure of) and then its just silence all the time. i treat her with respect and stuff but she dont she like talks with a whole bunch of guys when shes with me, i mean i dont talk to my female friends anymore cause i dont want her to think on what im thinking of her, im thinking that shes cheating on me with that guy she talks to the most, i told her this and shes like oh no im just friends with him and stuff im like wtf, and also in 1st period (i have her there too) shes always cracking up with this one dude and like when shes around that dude talks to me but when shes not around that dude completely ignores me. i dont know what to do anymore man i mean i really love her i love her a lot i dont wanna break up with her i almost cried when i wrote this i just want all this to stop! what should i do