It's all very well for your ex to walk out on you and leave you kicking yourself for all that has happened.
Partly your fault you realize and partly your ex's fault.
And much as you have tried you could not hold your ex back.
But you do want your ex back and how should you do it is what is troubling you.
Should you ignore your ex or run after them to come back? Would it make sense to plead with your ex to come back after all? Should you leave matters where they are and just get on with your life? May be that is a better approach to this split between you both.
May be you should be seen around in fun places enjoying the activity you're engaging in.
You should also be seen with new people.
As important as the new activities, is the new social circle to be seen in.
May be you could bring in a spark of jealousy in your ex by paying the same kind of attention to someone new.
This could be one dirty mind trick to keep your ex guessing if that somebody is your new found friend.
May be some of your conversation is overheard by your ex and will make them feel forgotten forever.
This feeling of being forgotten and neglected will make them forlorn and realize how great it used to be with you and that they have made a big mistake in breaking off with you.
Your ex will make whatever attempt is possible to reunite with you after this.
They will try to come closer to you or at least be in proximity.
They will find a way to be in the same company that you are hanging out in.
They will even attempt to call you and suggest coming back to you.
After this the ball is in your court.