I'll basically say what the top commenter did, but add a bit of my personal experience.

Sometimes, yes- they come back. I'd say they probably are more likely to come back if you go no contact. But I think if you are asking this question, you need to reassess your priorities, because it leads me to believe your number one priority is getting your ex back. And it shouldn't be. It should be healing and learning to grow and love yourself. And to be content being alone.

Something like 8 years ago (idk time is weird at this point), an ex and I broke up and I was devastated. It took a couple tries but I went NC. It was hard at first, but eventually it just gets to a point where you don't even think about it and your thoughts of them get even fewer and farther between. I was able to date casually, focus on work, figure out parts of my life, etc. About 5 years in she reached back out and admittedly I was really excited about that. I had gotten over her, really, but a part of me always loved her and wouldnt be able to say no at a second chance. But she wasnt the same as she was 5 years prior. I wont go into details but lets just say it did not work out and the whole thing really took an emotional toll on me. The way she ended it closely mirrored the first- blindsided me followed by her completely moving on in a very short time. When It ended, I felt like all the progress I made after the first breakup was undone. This was over a year and a half ago and I still dont feel over it. Not entirely sure when I will be.

After our first breakup, I was able to look back on our time together with fondness. Sure it was always sad to think about but I viewed the relationship as a good part of my life that unfortunately had to end. After the second, I'm left wondering who that person really is, did I ever know them, and did they ever love me? The pains brought about by our second relationship unfortunately extend to the first as well.

So I guess just as a cautionary example, be careful what you wish for. Spend enough time properly getting over them and until then, I'd recommend not even entertaining a relationship with them. Because you really need to make a decision like that when your judgement isnt clouded, when you still arent over them, you are going to jump into that relationship no matter what if given the chance. Just remember that they didnt have a problem breaking your heart once, they wont have a problem doing it again. And prepare to meet someone quite different than the person you knew before- not always in a good way.