How to tell if your bf is cheating !!?

Okay so my bf and I are both 14 and going into highschool. Before we went out this time we dated twice then took a 7 month break before we resumed the relationship, its been about a month so far. Before we went out (in general) he went out with my ex best friend for about a week before she dumped him (she told me at the time that she didn't even like him and she doesn't get why she said yes) anyways just a little backround info there. When me and my bf were going out the 2nd time she and her new friend tried beating me up in the hallway in front of his locker. He has always been overprotective but after that happened he became even more overprotective, after we broke up he punched his best friend then pushed him to the ground and started kicking him just for touching me and thretned my guy friend if he told me about (my other ex friend) (I've lost too many friends) talking sh*t about me. Anywaysfast forward about a month later ad I hear my ex friend ( his ex / my enemy/ girl who tried beating me up) talking abouther "flirtationship" with him and I never see him talking, the only thing I've ever heard him say to her was "ew, can't u see tha I hate u" then fast forward to now he has been really hot and cold hately, one day he's all lovy dovy and the next he compleatly ignores me ( started after some plans fell through) he left the freaking state without telling me ( only gon for a few days) and I had to find out from his siblings fb status! Then yesterday we were txting and he was being all cutesy and stuff and I txted something and he was like " wait is this *my name*"(he has my number) and I was like yeah who else would it be" and he didn't answer and I was like " or don't answer.." and he responded a half hour later "sorry" and I was like "thts okay, bbut. U nvr answered my question" and he was like "what question" and I was like "ughhh u know what 4get it nvr mind" and he didn't tlk 2 me all day yesterday after tht or 2day so far....help!