Why cant I trust my girlfreind

Im 16 and my girlfrieind is about 4 months my junior but we met through a friend and we sent pics or whatever and we liked each other so we talked for another month and a half before meeting and after the long cruel wait to see my love her birthday came so I went to her birthday party at her house I cam before her lol and she pulled up in a a car her sister got out and told me she was nervous or whatever so I went up to the car opened the door and saw her she was stunning to say the least we locked eyes and just kissed then I walked her out the car and into the house we spent that night making out and just talking sounds like a nice start lol but after about two weeks after the party her friends blamed me of cheating on her and I was not but after I got tired of being called a cheater I disconnected myself from every girl I used to talk to and( now keep in my she still talked to lots of dudes) then she realized that I really loved her. and she told me she was a virgin or whatever so the day we decide to have sex she did not bleed I was too caught up in the sex to notice lol but after the sex I noticed I just sat there I didn’t want her to think that I didn’t believe her so I didn’t say anything about it she later tells me she don’t know why she bleeds I said me to and that was the end of it I think this is where I started not to believe her. I love this girl but she talks to a ton of dudes and one day she asked me can a dude come see her the same night I tried to come see her but she said I couldn’t come because of her mom I said if I cant come how can a dude come she said some bullshit I was not listening but yea and she told me the dude supposed to be here at 11 so called her at 10:45 because I knew she was gonna try to see the dude but yea and amazingly at 11 she said she was sleepy and she never goes to sleep at 11 I was just like man whatever don’t call back I will be asleep and hung up on her and the next day I got on her page and saw her and this dude talking about hooking up and meeting up or whatever it hurt so bad to know that your girlfriend is trying to meet another guy I talked to her about it and she said she wasn’t really going to see him I was like ok whatever and after this she promised not to talk to any other guys the next couple weeks went fine but then I called her one day and we was talking having a good time or whatever and she puts me on hold but forgets to hit the mute button and she picks up the call on her house phone and its another freaking dude and they talk for like 10 minutes while im sitting there getting hurt they were talking about when they going to meet up or what ever when she got back on the phone she act like nothing happend and did I mention every time I get mad at her she gets mad at me right back then I end up apologysing before she stopped talking to dudes she would always text dudes in my ear and pick up calls and put me on hold while she talks to dudes she hurts me soo bad but I love her to death and cant imagine my life without her she don’t realize what she got please help me tell me what to do I cant take getting hurt like this =[