In grief, it often happens that you are almost numb for a short time, then the feelings hit home to you that.....this is for real, and it is over. Often this happens around the first month, when you feel very low in spirit and wish to be back where you were, whether it was good or bad.
My mum went thru this a month after my dad suddenly died, and my girls are there now after losing their dad a few weeks ago. It is a very hard time, and you need to do all you must to get thru the pain that comes up.
With a death it is easier because of the finality, the knowing that you cannot go back to what you had, and when you get thru the tears there is acceptance.
The loss of a relationship, no matter how bad or difficult, doesn't have that finality and you can find yourself looking at the possibility of reunion and starting afresh. It can be a miserable time, but I urge you to concentrate on doing things to help you get over this hump. Learning all you can about addiction, codependancy, grief and loss whether in books, here on SR and Ananon and doing special things you enjoy, can be a big help.
Know that you are not alone in how you feel, that there are many others here who are also struggling or have fought and won that same battle, and are here sharing their feelings, hopes and ideas.
It will get better, but it takes work, some self love and time to heal before it passes.
God bless