It could ruin friendships with the person of possibly even other friends.
When i was your age i saw so many people have week relationships and it didn't ruin anything, because they're not "forever and ever" relationships. Ending a relationship isn't game breaking stuff at 15 and below, it's practice.
When you get to sort of 18+ there's assumed knowledge in a relationship. A girl will assume that you know what you're doing, and you know how you're meant to treat her. If you limit your own social development,
you won't, and that should scare you.