Everyone has regrets. It's impossible to go through life without making any mistakes. And yeah, some mistakes have an impact that lasts for the rest of your life.
But the utility of regret is not to ruminate on what could have been. Regret makes you think about what you should have done differently, not to change the past but to change the future.
It's not about what you did, but what you are going to do. Regret teaches you how to act differently *now*. Learn from it, but don't dwell.