there are a few that are general that don't necessariy mean break up but here goes:
she ignores you, she suddenly becomes busy when you know she isn't really busy, the way she kisses you is different, she lets you meet new people or introduces you to them, she's mean to you, she doesn't like yoru style or doesn't like a particular thing on you, she begins the conversation with 'let's talk', she doesn't call you for a long time, she and her friends don't tlak to you often or anymore...those are a bunch of signs you know you're gonna go into break up
You know that its over when your you see that she has changed. The way she used to kiss you isn't the same anymore. The sex is different, or she just stops having sex with you. She is always late for a date. She gets mad for everything that you do She starts asking you what would happen the day you two broke up. Or things like that. And you defenetly know that its over if one of this days she stops comming home or you come home and find that her things are gone. But if you aren't living together then you know its over once she stops calling or leaves you a msg saying ITS OVER.
She starts acting different around you...almost as if she doesn't really care if you are around or not. It may even seem to be up and down, like one day she's acting like she doesn't care, the next or a week later there might be a day where its all good again. She also just loses interest in the things you do, and doesn't really want to spend as much time with you as before. She also puts her friends in front of you, and even wants you to hang out with your friends more...
Those are some signs that I had. Hope that helps. When this happens, if you still want her, you must remember to pull back and just give her room. This will give her some breathing room and help her think about if she really wants to lose you or not.
i totally agree with all of what deeplove55 said...but also don't think because one of these things are happening means its all. mostly likely if all of the above happens its done.