I'm going to snap at my best friend when she shares difficult things with me
I'm concerned at why do you think you need to slap at them?
I just don't want to hear that kind of stuff, and she's ruining my mood
You shouldn't snap at them. Instead, pull the aside and tell them want you are feeling and maybe recommend someone else in their life who can listen to them as they may really need to tell someone really important.
I'm going to get better at that stuff, it's just nice to know what is coming next.
It's good to be trying to get better for your friends. I do feel like you're really wanting to be this person's friend and that is why they like to tell things to you, I feel like you're really a good friend by exerting effort for it and helping them feel better about their issues.