I'm 15 and my girl is 15 as well. We go to different schools but still see each other every weekend. When I do see her, she tilts her phone screen and covers it away from me and when I did get a good glance at it, I noticed she had a few pics of guys shirtless that were not me and saw that she had been texting countless other dudes! I know she has a flirty attitude but I'm kind of whipped and sprung on her so its like I'm scared to rush into telling her how I feel. She's also been giving me signs that she's cheating like: taking random dirty pics of herself on her phone, keeping her phone and iPod away from me, texting a ton of other guys, getting overly dressed for school, having guys grab her and hold her at school and . What do I do? >email address removed per site rules<.

I would guess that she does it because she likes to flirt, she's 15, she's at a different school, and at 15, you shouldn't be so engrossed in each other that you exclude others anyway.
The fact that you are asking total strangers what she is thinking indicates 2 things: one is that you don't know how to talk to her in depth about such things, and the other is that you are naïve about life in general. I hope that doesn't sound like a put down, because it isn't meant to. It's typical for your age.
What should you do? Break up before you lose your integrity, because you are clearly 'hella whipped and sprung' on her.

I would say that you are the weekend boyfriend, and during the week she likes to mix it up with other boys. That she is so obvious about it, doesn't exactly make me think she's even friendship material, let alone girlfriend material.

She sends and receives inappropriate pictues on her phone, which is very risky business, and could turn out to be dangerous. She doesn't seem to care that she has a rep with many guys as being 'lose' or 'available'. She invites the attention of many males and doesn't slow it down even when you are home.

She is playing with fire and it is only a matter of time that she'll get herself in trouble.

I think you are wise to question her character, and her behaviour, and particularly question where you fit into a relationship with this girl.

That you are young, consider that this is a learning experience, and continue to keep your eyes open. Learn what you don't want in a relationship, which is pretty much what you described here, and learn what you do. Be very careful who you choose to have friendships with.

I would advise you to let this one go.

Get a girl you can be with more and share and care with. Even when she is with you she is somewhere else and that can't be fun. Whipped and sprung has you as a weekend pet.

She is who she is, but who are you, and why put up with all that kind of crap when you can do better if you wanted too. Over dressing for school is an old trick that kids use to fool their parents so they can wear the cool attention getting stuff at school.