There's going to be good days and there's going to be bad days. I used to convince myself that I didn't think of him anymore, but the truth was I thought of him every day, until I didn't. People say you need time, but you also need patience. Just when I thought I was finally getting over him, I started to dream of him. I would wake up in tears because of how angry I was that I was doing so good on moving on, yet all it took was one 15 second dream to pull me back 20 steps. But in order to move on, you have to let yourself feel every emotion and have patience.
Play it out in your mind. Have the full unabashed conversation like that person was standing right in front of you. Talk to them. Remember why you aren't together. If it was mutual, then this usually works. If it's one-sided, and your heart is broken, embrace it. Embrace the pain, remember, if there isn't anything you can do about the situation, the only thing you can change is the way you react to it. Amor Fati. Love your fate.
If this person you wish to "get over" has passed on, and everything in the world is muted gray, dull, and terrible, then in my experience, "getting over" is not something you should really even attempt. That person, as all people, are never truly gone from this world until they are forgotten. It is your duty to live your life as best you can, never forgetting them, but also living as they would have wanted you to. Go on adventures, pet dogs, eat strange foods, read books that challenge your beliefs, grow as a person, and maybe one day find love again. Knowing full well that they would approve.
I'm 40 now, and it seems the older I get, the easier it becomes to walk away from people. I've met the "love of my life" 3 different times, I've loved women without ever telling them, I've been rejected, cheated on, dumped, ghosted, married and divorced. I've had one night stands, and 12 year relationships. The only thing I can tell you is that the people we chose to love, leave pieces of themselves within us. Often times, you don't even realize it until you have the strange desire to go to an IKEA on a Saturday afternoon, and have no idea why until you walk in and feel the nostalgia of walking around with someone, laughing at odd chairs, and wondering why this insignificant thing meant so much.