I'm not going to spend much time with my girlfriend.
What is your reason for not wanting to spend much time with your girlfriend?
I really do not care about her all that much.
It's wrong to stay in a relationship with someone that you don't love. You should end the relationship if you don't have feelings for her instead of stringing her along.
Why do I have to feel bad about hurting her over something that doesn't matter?
You should not be with someone if you feel this way. There are plenty of fish in the sea, and you will both be happier if you break things off. Just be honest with her.