In reality, there are a few relationships that are unworthy of saving.
mentally unstable, you probably are better off without them. If the relationship overall was a good one, and they weren't abusive, and they were of sound mind, the following should help you and your ex get back together.
Pestering and pushing your ex isn't a good idea. If you try to constantly get in touch with your ex; whether its by phone, email, text message, or stalking them you're going to do more harm than good. They will see this as a sign of desperation. This could actually push them further away than bring them closer to you.
Don't argue, beg, or plead with your ex about your past relationship. It's easy when you and your mind are all alone. Your mind manifests all sorts of “wrongs” that you may have done. Even when your ex broke up with you they may have gave you reasons why. Now, you're probably beating yourself up over them. You probably wish you had never done those things. The past is the past. This is the present.
If you get it in your mind that the relationship is currently over. You can't go back in time, though you probably wish you could. Concentrate on what is going on now. The only thing worse than obsessively contacting your ex is to beg or plead with them. Make promises how you'll change, etc...This won't help you and your ex get back together at all.
If you would like some more great information on how to win your ex back.....
I have a friend named T. W. Jackson. T Dub authored a simple, down to earth step by step guide called The Magic Of Making Up. Take a look I think you'll like it.
If your baby left you, and you don't know what to do. Watch this little video, and you just might get a clue!