Consciously forgetting is one of the most difficult activities one can undertake. An example, in this case, is instructive.
Over the last month or so, I have realized that I consciously need to let a person go. They are not in my life at all right now and if fact have done nothing to sustain any sense of a relationship. The thoughts have all been on my side - thoughts that follow me around in my head and appear at the least usable times. It has reached the point that, for me, it is an energy sink. And so, I need to consciously forget them.
It is very hard, at first. Social media these days makes it all the harder. I will find myself suddenly doing a search on a search engine for their name, looking them up to see what and how they are doing. And then I will tear myself away and get back to what I was doing.
So I have to police myself. Every time I want to look, I have to say "no" and turn away. At the end of a day, I can say "Today, I did not go looking for X". Tomorrow, I have to get up and do the same thing.
Do I particularly believe that I can ultimately forget them? I doubt it, truly. I suspect the human mind does not work that way. But what I can do - what I am trying to do - is not make them my go to thought when I am bored or sad or bitter.
The only ghosts of those relationships that haunt my past are the ones that I continue to feed with my own energy. And only I can ultimately make them disappear.