The hardest part of letting go is finally realizing that there wasn't much left to hold on to.
Usually, by the time you make the actual decision, the idea has been banging around in your mind for a very long time.
You have obsessed about all the reasons that it has to end, made all the excuses you can , forgiving most of them, and tried to picture your life without him/her. You rationalize that this is the move you must make for your own well-being, but you really don't want to shake things up.
You like the comfort and stability of having someone 'there'. You argue that you'd rather live with them, than without them and so on and so on. You have a million reasons not to make the move and a million and one why you should.
You will continue, until you don't. That is all there is to it. All of the time it takes to make the move is necessary for your growth. There is no time wasted, there is always a reason for how long you stay. You are gaining some confidence, self-esteem or pride; or maybe you just need to get angry enough, whatever the reason, you go when you go.
It may seem as though you've made a snap decision, once you lower the boom; but the fact is you have been subconsciously planning your move the whole time. Usually, you will find on that fateful day when you walk out the door, 'that there wasn't much left to hold on to.' You had resigned yourself throughout the obsessing to that which you knew you had to do. And now you have done it.... good for you. As the relief washes over you, just remember, you don't find anyone new until you have the courage to give up the old.