Is my girlfriend cheating on me?

okay. im 20 shes 18. we just started going out again a few months ago. before that we went out for over a year. I know the first time we went out nothing was going on. we were broking up for a few months so i think that gave her time to meet some guys. anyway this is what has me worried. when she gets a tex and i go to pick up her phone to read it shes spazzes out and trys to take it. also she has a contact in her phone and the name is bestfrined. that's pretty weird huh? she talks to that one alot. like i said i never get to read it. one time i asked to read her phone so she took it and deleted the inbox and said here. and then there was only sent msgs. i dint think about going threw the sent. I just wanna know whats going on. if im getting played whatever ill move on i can care less. I don't like when people try to make a fool outta me. that's all