Most Helpful Girl
You can't get closure until you give that chapter meaning for yourself (ie: lessons learned together, ways you developed even with the bad). Let it go with compassion even if she was immature, everyone has the right to develop at their own pace. If she's making bad decisions for herself, that's her choice and she's not at her own rock bottom with it yet even if you are. But she decided to go it alone, and decided not to clarify. So you decide what your needs are in a relationship. Someone who will communicate with you clearly, someone open? Decide to ask for those needs to be met by the next person. Get out of the house and pursue a new interest or hobby so you can start writing the next chapter. Don't beat yourself up the days you grieve. Maybe put away painful reminders, avoid snooping or trying to re-engage a conversation. Because 5 years but no explanation, it most likely won't come, and you'll drive yourself crazy looking for it.
Most Helpful Guy
It's hard to get over someone you really like but if it's not meant to be then there's no point trying to force it. Best thing to do would be try and find someone new, or take up a new hobby to take your mind off it. After a while it will get easier but it will all work out in the end even if that means you do stay single. Chin up mate