Same. It's hard to remember things without something to jog the memory, and I like those memories, so I keep stuff. Just trying to keep memories doesn't seem pathetic or clingy to me. Something that would be is getting drunk and calling up your ex after years and asking to get back together.
Put everything in a box. Seal it, then sell it on ebay under the title, "Mystery Box". You don't tell people what they're buying, you're just going to say something like, "These used to belong to my ex. I don't want to just throw it away, but I also don't want to keep it. I won't tell you what is in there because half the fun is in opening it, but I will tell you that they don't qualify as trash and there is nothing illegal under Swedish law inside it." Then start the auction at a slightly higher price than it would take to deliver to China. Who knows, you can probably get a pretty penny from it.
Keep until new person comes? You wouldn't want your future married spouse finding your ex's stuff in a closet one day jump to conclusions.