Most teenagers in high school dream of finding their soulmate and wanting to find the person they're going to marry without realizing they have their whole lives ahead of them to find this person.
There's no rush to get married or have children, we live long lives and have more time than we realize to get these things in life accomplished. However, some people do find their soulmate at a young age and it can ruin the relationship finding them that young.
In your teenage years and early 20s, you're still a very emotionally immature person who hasn't figured out who "you" are. You're still finding yourself and coming to terms with young jealousy and pride. However, you think you're ready for this real, long love. But you're not. One of the saddest things in life is finding someone who you love unconditionally and who loves you back this way but you're both too emotionally immature and treat the other badly, whether that includes cheating or being toxic to them.
You don't realize the severity your actions have at that young age but as you get older you'll kick yourself for being like this.
Many people say to give these relationships "a break" and give each person time to mature and then reconnect the relationship but reconnecting the relationship could poison the person again. Being with that person you met when you were so young could bring back all those old, bad traits and make you a toxic, immature person and then you've both taken steps back in life and that relationship. Or you might get back together and you don't revert back to that unstable emotional place but you've both grown so much as people that you barely recognize the other person anymore and the connection is gone.
Sometimes, you just have to let them go.
Maybe a quarter of the couples who get together at a young age will stay together, through the growths and sorrows and tribulations that young love brings. It takes two very dedicated people to work through their problems and put their love first to make it. It's a lot of forgiving someone even if you want to just punch them and communicating effectively even when you just want to scream your heart out. It makes you emotionally grow up a lot faster than other people. You put this other person above all in your life and the reward can be so worth it.