I don't know what to do, I'm so sick and tired of my girlfriend and I can't stand being around her anymore.
Oh wow, that sounds really serious! Why did things get so bad between the two of you?
She's so negative and always complaining lately. I just can't seem to make her happy anymore.
I can see you're miserable. If you can no longer stand to be around your girlfriend, you should break up. Both of you will probably be happier.
Yes, I know I should end our relationship, I'm just trying to figure out the best way to do it.
Be gentle when you tell her, but make sure you're honest with her. She needs to understand why you're ending the relationship and that there are issues she needs to address in her behavior.