In advance I must warn you about the wall of text.
Maybe you feel like you and her were "ment to be...".
You don't have to feel like this. You only feel like this because you believe things that make you feel this way. If you believe that she was absolutley the right girl for you, and you and her were ment to be together, and it's a total shame that you aren't, you're gonna feel this way. But you choose to think that way... Think something else. I can't precisley help you out, but there are more girls out there, you just have to find one that 1. Adds SOMETHING to your life. She has to be interrested in you for her to do that. If she doesn't bring anything, why does she have so much value to you? and 2 (maybe this is kinda dubious) is hot\good looking\attractive in some way. But all men would probably agree with me on this to some point lol. I personally like girls that are fun, happy, have that aura around them, lol.
There are many girls out there that are hot. Women are everywhere, plenty of fish in the sea.
I think the most important point to remember is that you don't need ANY girls attention or approval. You ONLY need yourself! And your approval and love. If you like yourself, it doesn't matter if you screwed up, because you like yourself anyway, what's the deal? The only person who is ever gonna complete you is you, the only person who has to like you is you... You don't need ANYONE to like you for you to be happy. Control these emotions, don't be embarssed of them or anything, just don't let them take you over and control you!
When I say you don't need anyones approval, it's kinda different when maybe you're married or something, or your mom and dad, some ppl would argue that... I don't know, honestly. But for now I think it makes sence what I said...
I don't know if I hit the spot with what I wrote, because you said "I feel like I messed up", I'm not sure if I understand that very well... But it may be that you still want her to like you, or something, in that case I think my post is gonna help you out a little, or at least, make you think or realize something! In the end of the day, the best person to help you out is you tho, at least that's the kind of things I think for myself, and if you work in your self esteem, NOTHING women do/say can bring you down anymore. Just the mere sight of your ex ISN'T a reason to make you feel depressed! It's YOUR state of mind that YOU control in the end of the day, NO WAY that the sight of your ex can make you feel like this way if you don't let it!
I'm just gonna finish writing this post by saying this... It's happened to me too... I used to get infatuated by the mere sight of my ONS for quite a extensive period of time. These days are kinda passed now, I feel much much better, I haven't seen her since I changed some stuff on my way of thinking, but I think if I did it wouldn't happen anymore, altough I still haven't completley stopped suffering because of women... (Not in rock bottom anymore tho). I know it's super hard, believe me I think it's safe to say I've been in rock bottom a copule of times, but you don't have a choice, you don't want to feel depressed for ever do you? You (and I and everyone else) just have to find out a way to not let our states of minds be controlled by these situations anymore, and if we don't give up, we will. Thanks for reading, i'd appreciate if someone commented on me too, kinda like a bunch of dudes that may have some issues help themselves out mutually, I guess some ppl here can relate, it feels better to know you're not the only one... Or someone that was like this and overcame completley, some veteran, that's who's advice/motivational words would come real handy.