Summarize:

Although you may feel like you want to avoid the conversation or tip-toe around the topic, it is best to be direct with your girlfriend. There's no reason that you can't communicate with your girlfriend about what's going on in your head. Yes, this conversation may mean that she tells you she does want to break up, but it could also mean that she tells you what's bothering her, and that she doesn't want to break up. Either way, at least you will know. Tell her you want to set aside some time to have a conversation about something that is on your mind. Don't just walk up and ask her if she wants to break up. This may confuse her, or cause her to react defensively. If she says she can't talk because she's busy, suggest a time when you know she isn't at school or work. You could also try inviting her to coffee or lunch, that way she will see it as time that she sets aside to talk to you, rather than an impromptu conversation. If you aren't able to talk in person, you could also try chatting on the computer, over email, or over the phone. If you make yourself available to her over multiple channels, she will eventually have to give you a few minutes of her time. It is important to take time to stop and think about your reasons for suspecting your girlfriend of something, rather than jumping straight to a conclusion. Consider what evidence you have for the suspicion, how realistic the suspicion is, if you can verify the information somehow, and what you should do with the information. For example, you might suspect your girlfriend of cheating on you because you saw her smiling and laughing with a coworker. However, if this is your only evidence, then you might consider whether she was just being nice and trying to pass time at a somewhat boring job. You might decide that the best thing to do with the information is to ask her if she has any interest in this coworker. Avoid saying things like, "I know you want to break up with me, and I know it's because of that guy you've been hanging out with. Why don't you just get it over with already?!" You're assuming things, and although you may be right, throwing accusations in her face will only make her defensive. Instead, try approaching the conversation by saying that you sense that something has been on her mind, and you'd like to understand if she is happy in your relationship or whether there are things that need work. You can also say, "I feel a bit worried because I've noticed that we haven't been hanging out much anymore, and I'm not sure if there is something bothering you." This shows her that you are trying to express your own feelings without accusing her of something specific. This is called nonviolent communication, and is a great way to approach difficult feelings with people you care about. Active listening is when you use body language, questions, and other techniques to increase your comprehension of what your girlfriend says while also sending a clear signal that you are listening closely. For example, you can silently repeat what your girlfriend has just said to help yourself understand it better and you can increase her sense that you are listening by maintaining eye contact, nodding, and saying neutral things like, "uh huh" and "yes." Don't just jump to your own conclusions, and resist the temptation to interrupt the things she is saying. Give her a chance to explain why she wants to break up, or why she doesn't want to break up. She might have very legitimate reasons why she has been behaving strangely, and you will come across as insecure if you aren't able to give her a chance to talk to you. If she does want to break up, it's still important to listen. The reasons she wants to break up may be things you hadn't thought of, or hadn't noticed. You may realize that breaking up does make sense. It is also possible that she does want to break up with you, but doesn't want to hurt your feelings. Therefore, it is important to try to really listen to what she is saying in order to determine what she is really trying to tell you. If she gives you lots of reasons why she doesn't feel happy about the relationship without explicitly stating that she wants to break up, try to be a bit direct. You can do this by saying, "It sounds like you're feeling really unhappy about the relationship, but maybe you're afraid of hurting me. I'd like it if you could be honest. Do you want to end the relationship?" Hopefully she will be honest with you at this point. Now you have a chance to get anything off your chest. If she has said she wants to break up, it may be tempting to say mean things, but try not to do this if you can. It doesn't solve anything, and won't make you feel better. If she has said that everything is OK, then tell her what has made you feel worried about it. Make sure that you use "I" statements rather than "you" statements when you talk to your girlfriend. "I" statements are less likely to put your girlfriend on the defensive. For example, your girlfriend might become defensive if you say, "You have been acting strange. You need to tell me what is going on." Instead, you might say something like, "I have been feeling some distance between us lately and I was wondering if you felt that way too." If she breaks up with you, you don't have to say anything if you don't feel you want to. You can get up and walk away, or just say, "OK, I understand." If you want to, you can also tell her your feelings about the break up (e.g. that you're sad about it, that you're mad about it, or that you think she's right, and that it's a good idea). Anger is a normal emotion, but it can be hard to control sometimes. It can be easy to become defensive in a conversation where someone might break up with you. This is because being broken up with gives us a feeling of rejection. You will likely feel like you want to get angry in order to protect yourself from your own feelings, but getting angry is unlikely to help the situation. Try to focus on keeping your voice even and low, and your breathing even. If you feel like you can't help but get angry, consider walking away from the conversation. Even if she says she wants to break up, and you feel like you hate her right now, walking away can help keep you from saying things you don't mean or that you might regret later. Whether the outcome of the conversation is that you no longer have a girlfriend, or whether it means you are still together, accept what she has said. If you break up, then it's time to start dealing with the break up. If she says she's happy and doesn't want to break up, believe her. Don't constantly question whether she wants to break up. This will be annoying, and it will make you seem insecure.
Tell her you want to talk. Don't make accusations. Listen to what she has to say. Say what you need to say. Try not to get angry. Accept the outcome of the conversation.