Darragh asks: "My girlfriend and I were together for a number of years, and then I really messed up. I've tried calling her, texting her, showing up at her house, talking to her friends.. and she's just asked me to leave her alone. I can't get her out of my head though. I just want her back! Help?"
When a relationship ends, regardless of the reason or fault, we all feel a gap in our lives. You're struggling with that gap Darragh, and that's what's fueling your need, almost desperation, to get her back. Let's look at how you got here, and what you can do about it to get back on track again - which may or may not include your former partner.
We're going to start with what not to do after a breakup, which in your case means you have to stop beating yourself up over whatever you feel you "messed up". All you can change is the here and now, or how you react in the future. That may mean reviewing your actions and coming up with a plan to ensure you react differently in the future, or forgiving yourself and accepting you did the best you could under the circumstances. It's cold turkey time though; if you need an elastic band around your wrist or a good friend to remind you every time you start on this tack again - do it.
Next up is breaking some bad habits that you (seem to have) adopted post-breakup. I strongly urge you to read the article I've linked to in order to work through this step. In a nutshell however, you want to look at any behaviors, actions, events, people or things that aren't serving you anymore, and like an addition, remove them from your life. How to remove them is the next step; we're just reviewing what they are at this point.
If you actually worked through all those steps (they'll take you a few weeks at best, a few months for most people), I'll hazard that you likely feel differently about your partnership now. Like I said to a dear friend recently, who broke up with his girlfriend of five years, "If you really want to see if she's The One, you have to take a long break from one another. Six months at least. Give each other some space and time to figure out what went wrong, what needs reviewing, how you can be a better you. If after that point you're still questioning her Rightness, then, and only then, do you make contact to go for a walk-and-talk".How do you remove anything from your life, especially if you've got a lot of emotional attachment to it? You fill that space with new things, things you love, things that give you an even stronger emotional pull towards the positive. More concrete ways to feel better after your breakup include doing the things again that you stopped doing while in the relationship, finding new hobbies you're passionate about, getting sweaty with a good workout, or traveling somewhere new and exciting.
My friend has yet to heed this advice, even though he's agreed it's sound, and I'll readily admit I've struggled personally with the same situation. The fact is, if you want a better, new relationship with someone you love, when there's history and it didn't work out positively in the past, you've got to take the time to focus on you first. Center yourself, calm yourself, inspire yourself to new heights. Review what you want your life to look like,what your ideal partner embodies, how you want to feel when you know you're mutually and madly in love. With some space, distance and time, you may well realize that that person is someone other than the woman you've written me about - or you may realize she's still The One in your heart. Either way, you'll have a clear answer, and all that you'll have to do is move towards whatever makes you the happiest.