How do you win back an ex-boyfriend whom you are going to see Friday night if you don't think you should ever have broken up?

You didn't say if he broke off with you or you broke off with him. You also didn't explain why you are meeting with him. You have to decide in yourself if you are in denial and what you think is still romance or if there is still some love there. The worse thing you could do is corner him. Don't put ANY pressure on him to continue on with your relationship. Talk about whatever you two like to talk about, but keep the conversation light unless he goes into the direction of getting back with you. Smile, be calm and act independent without misleading him into thinking you aren't interested in him. Sounds like a tall order and it is! Good luck