This question is repeated on forums like this all the time. Here is the truth:
1) if you dated someone and you parted ways, and you think about them on occasion in a good light - you were compatible but it wasn’t a perfect match
2) if you dated……….But you think of them constantly guess what? That was your person. They were it.
I’ve been around plenty of people and observed this happen. The one that got away that is always on your mind is the one you should have been with.
You’ll never be settled without them. Don’t *censored* it up. You’ve got one life. Give that person from your past a call and tell them how you feel.