I know you have a hard time talking about how you feel. I know you also have a hard time listening to a bunch of mush or inspirational bullshit. I'm going to respond on paper, too. That way, when you get to parts that make you sick, you can put it down. :) It works out for me, too. I don't have to worry about getting bitch-slapped for being corny.
I'm going to do this line by line from your letter.
1) "Luck" or "destiny" or "god", whichever you believe in, plays a part every single time you go on patrol. It determines which demons you run into. It determines how you feel on the nights when you run into the Big Ones. A lot of times, I think it's more important than skill. Think about how many fighters are evenly matched. The winner isn't better. They just get the "lucky" shot. Another night, the fight would go a different way. If you ask me, the simple fact that Katherine packs a gun shows she doesn't trust her skills the way you trust yours. It's a rigged fight. She's a hunter who cares all about the ends, none about the means, which I guess makes sense because she's soulless and can't feel guilt. She ought to be ashamed to "beat" an old adversary like that. It's worse than a runner on steroids.
2) Guilt for whatever you did... Babe, it's just baggage dragging you down. Feel it for a little while. It's what makes you a good person. Then cut it loose. If I know anything, it's how useless regret is. The only thing that makes wrongs right is making up the balance in the future. If I had stopped rolling around in regret and did the right thing last year, I would've been on your doorstep sooner, begging to get you back, instead of wallowing at home. What good is regret? Nobody benefits from it. Action will make you feel better. Decide what will come closest to making up the wrongs you did. Do it, and let the past go.
3) Regular humans like your neighbors -- the ones that aren't used to the supernatural yet -- are afraid. Sometimes I think we do ourselves a major disservice, not getting on the media and telling our side of the story. We (meaning the white hats) just bury our heads in the sand and pretend the whole thing's still a secret. Misunderstanding breeds fear, and that's what makes people distrust us. They just don't GET it. So people like Katherine swoop in and tell the story their way. We should teach them. Instead, the vampires are on TV, spreading all kinds of garbage and eating up the limelight.
4) You fight to save assholes like your neighbors because they're like kids. They're helpless (some of them are even idiots). Powerful people make them feel more helpless and idiotic. They bully you because you're different, but even a schoolyard bully needs his ass saved sometimes. You fight to save all the people who AREN'T assholes. There are more of them out there, Kris. We just don't notice them because they're not making all the noise.
5) When you don't want to help people? You stop for a while. I think apathy's dangerous. It means you need a break. You go out on the street not caring, and you get hurt. What would you rather do? I don't care if it's basket-weaving, you should do that for a while. You've been slaying a long time. You've earned a break, even a retirement if you want one.
6) I'm actually surprised your family didn't notice you were gone (I bet Rosa did), since they lean so hard on you all the time. But if they didn't, you know what? It proves something, Kris. It proves they can make it without you. It sets you free! You don't have to feel guilty anymore. You don't have to pick up all their slack. They just proved they can manage without you pretending to be Hercules. This is a fucking break-through! You say the word, we're out of Chicago. Just pick up and go someplace else. What do you want to do? Where do you want to go? We'll go.
7) There's always gonna be somebody to look after you. I might not be a superhero, but that's why I'm the right guy for the job. You're my girl. You're my family and my best friend. Put the weight on me, I can take it.
8) People who feel deserted or alone look for comfort in the wrong places all the time. Sometimes it's chemicals, sometimes it's bad habits, sometimes it's people. You reach for what's available. The one person you could reach was Katherine. I know it feels sick. I'd feel sick about it, too. She took everything from you, but she was also the person giving you food, water, shelter. Weird things happen in people's mind in conditions like that. It's just Stockholm Syndrome.
9) Everybody, slayers included, needs to be reminded that they're human once in a while. I'm not okay with the way you got reminded, but it's necessary. You've gotta remember you can get hurt, or you get careless, start thinking you're immortal. This is the kind of experience that gives you a good glimpse at the life you want to live. If this isn't it, don't stay in it, Kris. If I'm not it, it will fucking break my heart, but I'd rather you know that now than start feeling like you're responsible to me, too.
10) The lesson you teach your Slayers is that everybody falls down. You get back up and dust yourself off. You don't let it kick your ass twice.
11) I fully support your decision to stake this bitch. Just don't get crazy and take out a city block, too. Wait. You maybe just did that. :)
I know I've got an annoying way of dismissing all your fears, or coming up with reasonable excuses for everything you do. I rationalize. I'm sorry. I'm not trying to diminish anything. I just want you to know you're not a bad person. No matter how you turn this thing over, I can't see it as you doing anything wrong. You could do what Katherine told you to do, and sacrifice a few jerks, or you could live to see another day and save hundreds. You made the right choice.