You don’t. You get over it and move on.
Life is far too short to waste your time and emotional energy trying to prove to someone that they were wrong to let you get away. We all get rejected in life, and we can’t dwell on it. That time and energy is better spent moving forward, living your live and finding someone else. If this guy sees you happy and in love with another man, then he’ll probably realize that you were a catch that he should’ve caught. Like they say, living well is the best revenge.
On the other hand, he might have had a good reason not to get with you. Maybe he just wasn’t into you. Maybe he knew you were not right for each other. Maybe he’s in love with someone else. Does that make him a bad guy who needs to be taught a lesson? Nope. He made his choice for whatever reason, and that’s his right.
You need to let it go and focus on the future, not the past. It’s over. Move on.