I don't know how to react or if I am just worried? HELP!

my bf and I have a meeting spot after school and I was going to meet there when I found out that he had skipped school to go to some girl's house and I would have been ok with that if i hadn;t known that he has hooked up with this girl before and he didn't want me to know about it. so when I got home i called him and he said that he wanted to tell me but he was afraid that I would get mad and kick his ass and I told him that i was just hurt that he would lie to me he said he wanted to tell me but he didn't want me to hear it from someone else. then this same girl spent the night at his house with him his brother and my best friend I would have been there but I was grounded. but he said he slept on the bed by himself. also this same girl went over to his house and brought a friend that liked him and she went and sat on his lap and asked if he wanted to hook up but in all of these incedents he says nothing happened and that it's all about trust. but I am noticing that ever time this girl is around something happens but she has known him longer than I have and she seems pretty cool but I don't want him to be tempted but then i am afraid that he will think i am over reacting and don't trust him and am trying to choose his friends for him and that is the last thing I want him to think but at the same time i don't want to have to worry that next time I am not with him and he is with this girl that something will happen. but he has never cheated on me.

Well I want to but I am afraid that he will get defensive, and we usually don't fight except about little stupid things and so he is a nice guy and I love him and he has never made me cry but I just can't shake the feeling that something COULD be going on but he has never given me a reason that I could prove not to trust him but it really makes me wonder.

i dont know how to help you on that one sorry any one wanna help me READ (i need help on a relationship problem) and see if u guys can help me