Yeah I think we've both changed a ton from who we were when we met but we've both become better people, so either we're lucky or we just have a healthy relationship

This is more likely at a young age, i.e. teens into 20s. If you meet your partner in your late 20s and up, they're unlikely to change in significant fashion. Important to consider in pairing with the advice that you can't change a person. Expect a douche to remain a douche.