Now that you have broken up with your ex, all you have left are memories of your time together. It is a regular occurrence for relationships to end but irrespective of the circumstances under which the break up happens, it still hurts to let go of what might have been.
Those days when you are at your weakest and you feel like seeing your ex again and maybe even restarting your relationship will surely come. Some memories you have had with them will surely haunt you but this is not the time to run back them, most especially if you are now in a new relationship.
Even if you parted ways on good terms, there are boundaries to what you can now do together (after all the breakup was caused by something). This is not only for your own sake but also for the sake of other people in your lives.
If there is any hope of reconciliation at all, you both will have to trash it out properly but while you are still calling yourselves ‘exes’, these are the things you should not be doing with your ex anymore