I'm pleased to hear that you don't gossip.
I'll tell you how I would feel if I were Katherine ~ just based on what you have stated.
He seems to like me, but he seems to like her, too.
If he really liked me, he'd ask me out ~ am I really his girlfriend or not?
Does he like Kelsey better, perhaps?
She is trying to make him interested.
She must be laughing at me, while she is criticising me to him and I'm over here looking confused and miserable.
Of course, I don't know Kelsey or Katherine. I don't know what sorts of personalities they have. I don't know how they feel about each other.
Girls have a tendency to try to out-do each other when it comes to boys.
When I was younger, one girl used to sit by my boyfriend, leaving me to either sit elsewhere, looking like a gooseberry, or make a fuss and look desperate.
Another used to go on about how much she fancied him.
How do you think I felt?
Yes, it was nice to know that I was the one he had chosen, but I still felt awkward and a bit foolish. It's a bit embarrassing to have to pretend that it doesn't bother you, whilst another girl is trying to take your boyfriend's attention away from you.
But you may well be too young to be 'going out' anyway.