Breaking up is an emotional roller coaster ride and it shouldn’t be initiated over the slightest of things.
“While we are free to choose our actions, we are not free to choose the consequences of our actions” – Stephen R. Covey
All anyone can do is apologize and explain. Explaining entails what you were thinking/feeling and what you now think/feel. It also should include what you have learned from this experience and how it will help to pave the way for a different and better relationship if given a second chance. The rest is left up to the person listening.
Don’t be surprised if they need some time to let things digest before making a decision. In fact you may wish to tell them to take some time and get back to you. (No pressure) There still is no guarantee.
I’ve never understood the desire to go backwards in life. (I believe in putting everything you have into a relationship when you fall in love.) If it doesn’t work out there is nothing left for you to offer a second time around. (There is nothing better than your best.)
Can the future be so dim that you believe the best thing you will ever have in your life lies in the past? This is not exactly what one would call having a “positive outlook” about life. Whatever happened to "Everything happens for the best"?
Regardless of who dumped who, time heals all wounds. An ex is an ex for a reason and it’s usually a very good reason! Move on. You can't get to second base if you keep one foot on first!
Your future lies ahead of you and not behind you!
Best of luck!