I regret breaking up with my ex. What should I do?

Have a nice quiet alone time with yourself. Make sure you want to take the venture out to going back to your ex, because you broke up for a reason. See if the reason was a valid one in your book and if you still feel it was a mistake; then by all means take a time to have a face to face discussion with your ex and see where that leaves the two of you.

Think about what you want. Think about why you're missing them. Is it because you're lonely, or because you genuinely want them back in your life?

Talk to them. Explain what happened, how you felt afterwards and why you regret breaking up with them, why you want to be together with them again

Try talking to him/her and say how you've been feeling! Maybe they share the same feelings as you, because they weren't the ones who chose to break up.

The most important thing after a breakup is to give the other person some time and space to think. You should use this time wisely too, find an alternative distraction and find something creative to do to turn any negative thoughts you may be having into positive ones. After that, writing down how you feel is a good start, and then you can be completely honest about how you feel with your ex, tell them how you're feeling once you have given them the time and space you need, they might not want to get back together, but don't let that deter you, a good friendship is the best possible thing that can come out of a situation like this :D

Ask yourself if you really miss him as a person, or you just miss the relationship, having someone, os having something stable.

I feel as thought you should try talking to your ex, if that doesn't work. Try to refrain from contact of wanting to get in a relationship and just stay friends, and see where it goes from there.

That will be determined by led to the break up, if it is something fixable that you overacted on without being rational then you can request to meet with him and apologize and see if he is still available for and willing to fix things . If he has moved on already then learn from the mistake and make sure that you do not repeat it in the next relationship

well then you should call them and and fix the situation if they are willing to do that and have still feeling

Sometimes we can feel feelings from our past... Sometimes these are residual, sometimes these are merely results of habit, sometimes it's a residual flame, and sometimes it's comfort in what you previously knew... But the truth is, you know what is right for you... You know what your should do... Maybe that's playing a song from a boom box outside their bedroom window like in that movie, or maybe it's getting back into a saying scene... Be cautious, friend, but don't be afraid!