As someone who has successfully dealt with EXTREMELY bad alcoholism (over a fifth of vodka a day), I feel I can offer a few tips for you. Whether they will work for you personally or not, I cannot honestly say.
The first thing I found worked for me, is to find the rationality behind my own actions and not what I resort to out of emotion in the current moment. Our mind loves to play games with our bodies, and when you can learn to control that you will start to find yourself in the drivers seat again.
My second words of advice, are to identify the things that trigger you into reminding yourself of those past thoughts, in your case a relationship. Isolate and identify them. When you learn what leads you to a bad train of thought you will have a better point of view as to what is making you think in such a detrimental manner. "What makes you turn to these thoughts, and why?" If so, do your best to avoid them and as I will say for my third and final piece of advice: REPLACE them.
Once you are able to identify the places in your mind that make you think a certain way and learn how to avoid them, you will find yourself with what seems to be a void inside of yourself. Try to find positive activities that do not remind you of the path you once walked, and do your best to slowly implent them into that spot your life. When I say slowly, do it in just that manner "SLOW". Simply replacing something in an instant will always cause you to feel off. For example: if you went and got a fancy new leather couch you would instantly think of it every time you walked into the room. Try to replace old habits with new, productive ones in a way that makes you truly feel comfortable.
Any addiction is not an easy thing to tackle, but with diligence and repetition, you will surely find yourself feeling better.
Also, don't forget there is always a network of support for you to confide in, so use it to your advantage. You will be surprised at the willingness of others to offer their assistance in times of need.
Stay strong!
