If you think you've found the one, just don't let her go. And if she really is the one, then you'll know. That shit rhymed lol no but for real, any girl you can move on from with no problems obviously wasn't the one, but if the girl is worth chasing after, shes the one lol
What do you mean just don't let her go. If she want's to go there is absolutely nothing you can do to change her mind, it's up to her only. If you keep bothering her she will just end up losing respect for you, and you will end up even worse than just left alone.