I found it most satisfying to throw away everything from past loves that I didn’t want to keep in my life, which I did last summer when my dad made me clean out my closet (I hadn’t lived there in 6 years). But I have a problem emotionally holding onto things, so I think it was theraputic in my case. I never looked at them, but their presence made me feel attached or at least not let go completely. Then again, the things I learned from them always stay with me.
Keep them. It doesn’t take up much space if you file/store it correctly. You won’t regret keeping them, but you might regret losing them.
I am glad I kept all the letters from my high school boyfriend. 11 years later, we met again, fell in love again, and we are together now and I am about to move across the country to live with him. The letters from him are invaluable, and I am very glad I kept them.
As I have been packing for my move, I went through all my other letters, and it was a wonderful walk through memory lane. I will never give them up.
Keep them!! I’m with Jonathan Chance here - someday someone will want those as a piece of history - a window into one 20th and 21st century person!
I have several flat plastic containers with my old pictures, clippings and magazine scraps from HS and college. They also contain all the journals and diaries I’ve kept over the years. I plan to be a veritable treasure trove for some historian in years to come! 
Keep them - and keep them in their original form. Think of the future historians! Seriously!
That doesn’t mean you should close the door on it.
I keep all old letters and things. Some of the coolest mementos I have are old cards, poems, drawings, etc. from old friends and lovers. And I have some interesting correspondence from a guy I knew who was in the army. I can’t imagine throwing all of that stuff away. I would miss it for sure.
The less insight historians have on my romantic life of women other than my future wife, the happier I’ll be.
I scortch all evidence of my past love affairs: photos, letters, notes, gifts. Once the love has all gone sour, I want no physical reminders, ever.
If I must think about a girl, the right song or food will do. Every woman I’ve seriously been with has one “assigned” to her.
I’m way too disorganized to keep anything like this, so it doesn’t come up for me.
I’m glad I’m not the only one like this. I read these threads about how future historians will want to read letters written by people now, then think about the notes and, later, emails that my friends and I exchange, and I think I must be really shallow or boring or something.
Wrong! It’s nice to have a bunch of exciting stuff about storming the beach at Normandy etc…
But it’s the day-to-day stuff that’s most useful to historians. Knowledge about how people actually LIVED is what makes history seem alive.