Like a Pensieve, but for people who actually exist.

So, I do this thing every morning and every night called “freewriting.” It's a concept that was originally introduced in The Artist's Way by Julia Cameron, where she proposes it as a prewriting technique in which a person writes continuously for a set period of time without regard to spelling, grammar, or topic. It clears the mind and promotes clarity, which then introduces more raw creativity into our lives. While it was originally introduced as a writing tool, it's also been seen as extremely helpful when it comes to meditation, spiritual study, life coaching, therapy, etc. 
Basically, like this girl once said, it's basically a shower for your brain. 
Whether I realized it or not, I've been applying this concept to my life for at least a decade. Especially when trying to work out the emotional stuff. I used to write them as letters to my exes (“Why did you have to be such an asshole all the time? Why did I still love you anyway?”) and then would either promptly delete them or plant the thoughts into some other form of writing. Now they've evolved as sort of a daily check-in and clearinghouse for what I'm feeling and processing through on a daily basis.
And yes, you can call it a journal or a diary. It's basically the same thing.
The difference, though, is whether or not you want to keep it. I kept a log of my freewriting when I lived in the woods last summer, and I am so, so grateful that I did. The beauty and peace and learning that seeps through the words that I wrote then is still astounding to me, when I re-read them a year later. And as I'm going through this particular experience, I want another log of a different kind – I want to be able to go back and see what I was doing that worked and what I was doing that didn't.
And I also want to be able to look back someday and see how far I've come.
But when it comes to other forms of freewriting – like Truth Telling Letters (letters that you write to someone that you need to forgive) or the really heavy, emotional, dark place stuff – I find that it's actually kind of cathartic to delete it. First, it's incredible to just write it out. Whether they're rational thoughts and feelings or not, if they're circling around in your head, they still need to be validated. And there's a certain power in being able to record those thoughts so you can start to take a step back and then reframe it. It never fails that whenever I'm in a dark place and I write a bunch of shit about how much things suck right now, how awful I feel, etc, I invariably start to write a pep talk for myself at the end. It's as if those dark thoughts and feelings are holding me hostage, and once I get them down and out on paper, I'm able to free myself from their shit-talking attitudes and start hearing the things I want to hear. 
Like this morning... I'm in that stage right now where I'm having dreams every single night about him. And dreams with him are the only ones I'm having. And they're awful. They reflect every single shitty feeling I'm trying to work though right now - feelings of being undesirable; feelings of fear that love is always conditional based on how pretty, thin, or successful I might be; feelings of anger that I let myself trust someone who let me down. Pretty shitty stuff, yeah? It's hard enough to confront those feelings in the broad daylight, but then to be trapped in a scenario that illustrates them during the entire sleeping night? Fuck that.
But like most powerful dreams,  I know my subconscious is creating them in order to send me a message. Either I'm not totally confronting these feelings yet and I need to be, or I'm confronting them but still allowing the same ending to happen over and over. So this morning I flipped back the covers, got out of bed, and wrote a few pages describing the dreams and how they made me feel and why.
And here's the thing: It's not easy. Admitting your worst fears is scary and hard and way less fun than browsing Pinterest. But it is true that the sooner you confront your fears, the less power they have over you. And once I do it, I always see the flaw in those fearful beliefs. And then I'm able to turn them around into beliefs that I want to have. Beliefs that reflect a great self-worth, a general foxiness, and the knowledge that broken trust doesn't mean that my trust-o-meter has to be permanently broken...it's just in the shop temporarily for repairs.
So try it. Try it especially when you start to think the same thoughts over and over (“How am I ever going to trust in love again?” "What if I never get laid again and I'm doomed to roam the earth, sexless and alone, for the rest of my days?" etc). When a thought keeps repeating, it's because something about that thought needs to be examined and studied. It's coming from a place that you're either willfully ignoring or don't understand quite yet. And thoughts like those are like bad credit ratings – you can't improve what's there until you understand why.
My suggestion is to try a morning or night freewriting practice for 5 minutes. That's it. Get your thoughts down on a page in the morning or night (whichever works best for you that day. Maybe you do both on a particularly head-tripping day. Up to you. It's not a diet – you don't fail if you decide to do it differently each day) and then decide if you want to keep it or delete it. Don't worry about the content or the spelling or whether you even finish your goddamn sentence...that's why it's called freewriting. It's free form: just get out whatever is coming into your brain. 
The only guideline I really suggest adhering to is this: If it's really heavy stuff, even if you're going to delete it when you're done, try to end it on a positive note. It could be something as simple as “You know what, this really fucking sucks. But hopefully I feel better tomorrow.” You don't have to try to bury yourself in rainbows and unicorns if that's totally not where you are right now. The whole point is to get real with yourself and what you're really feeling/thinking so you can free yourself from it (get it? Freewriting makes you free? GOD I'M GOOD WITH THIS STUFF) and get closer to the stuff you want to be thinking about.
Like, what a total Super Fox you are.
Or, how your life is honestly going to get better and better with each passing day.
Or, how you never realized how strong you were until you went through something like this, and came out winning.