You're looking through your wallet or purse in search of something specific, but suddenly your train of thought is diverted when you come across something. You come across a movie stub, concert ticket, parking pass, etc. To anyone else, that would just seem like something you forgot to throw away, but to you, it brings endless memories rushing right back into your mind.
You have done your best to forget him. You do anything and everything to not think about him. You do what you can, but that small item makes you remember. You might just brush it off like it's no big deal or you might sit there for a minute and feel tears come to your eyes. It makes you sad because you remember all of the good times you had together before something went wrong. It makes you sad, and that's OK.
It's OK to miss him. He was such a huge part of your life for a long time, and for a while, you were unable to see yourself without him. Missing him doesn't make you weak, and it doesn't mean you want him back. It just means that you loved the person he was, and you enjoyed the times you had together. He was and always will be a main character for that chapter of your life, and that's OK.
When times like these happen, don't keep yourself from missing him. Do it. Miss him. Remember your first date. Remember the times when you were driving down the road singing together. Remember when you were watching him cook, or when you were chasing each other around the apartment and you couldn't stop laughing. Remember those times and use them to remind yourself that even though it may have ended horribly, your relationship wasn't horrible. Of course there were fights, but you were happy.
If you don't miss him, then it may be that you never truly loved him. Missing him means you cared. It means you gave a part of yourself to another person, and you were vulnerable. There is nothing wrong with that.
When you come across something that reminds you of him, give in to missing him. Give in because it's normal to miss someone you shared so much of yourself with, but don't disregard why things ended, and don't let missing him consume you. Miss the person he was, not the person he became. Forget the man he turned into and forget the pain he caused you. It's not worth keeping that in your mind.
It's OK to miss him. It's OK to want him to miss you. It's OK to miss the happiness and love that filled your heart during the time you shared together. It's all OK.