"But is it just you can't take it any more, or do you feel differently about me?"
You are torn, as you do really like Kara, and because of that and your general principles, you don't want to mislead her. But you also want to cum so desperately that you don't want to screw up your chance with her.
So you say that you have been thinking about her a lot today, and that you want to make her as happy as possible.