I am not aware of how long it has been since your breakup but letting go takes time as getting over is not a simple process. You must realise that the past had some important lessons which you must learn, there will always be good things and bad things in a relationship but an equilibrium has to be maintained which is decided by you and in this case you have made your decision. Every relationship is different and will have its own dynamics, so take your time if you are not ready.