I'm not going to spend time with my girlfriend
That feels very sad, why don't you want to spend time with your girlfriend?
I just don't like to spend time with her, okay?
If you don't like spending time with your girlfriend, why are you even dating her? If you're involved with someone romantically, then you should be enjoying her company. Maybe you two should break up.
I want to dump her.
It's probably for the best that you're thinking of breaking up with your girlfriend as you seem to no longer be interested with her. I suggest you still do it in a calm and respectful manner so that you don't hurt her feelings.