One thing you could try is not fighting it. When you get reminded, just note that you are being reminded in an “isn’t that interesting” kind of way. You’re probably not going to be able to stop it. If you live with it, you can learn to get along with it. It’s there. It hurts. It’s not going to kill you. You just kind of set it aside, in a box up on a shelf, and you catch a glimpse of it every so often, but mostly it’s not in front of your consciousness.
When I was depressed, I used to try to fight my ideas about how worthless I am. I couldn’t do it. So now, I just try to notice that I’m feeling worthless, and not be really attached to the idea of becoming worth anything. Whether I think I’m worthless or not, I can still live my life. Little changes in my life based on what I think of myself.
You can live your life whether you think about this person or not. Those thoughts are just a part of your life. The relationship was a part of your life. You were there, you were hurt, it still hurts, but that doesn’t have to keep you from living your life. Perhaps it already doesn’t keep you from living your life. Don’t worry about stopping the thoughts. That isn’t necessary, if you can allow yourself to have the thoughts and not really make them into something that is so important.
For me, it’s like just not thinking about something. If I think about it, I’ll make myself worse. So, when the thoughts come up, I notice them, but I don’t indulge myself in them. I just turn to other things, and gradually those thoughts recede until they come back. It’s a hell of a lot easier than fighting something I can never seem to beat.