Here's a problem. People see someone elses story and think of it as a template from God. God worked in that mans life that way because that's how God chose to work in his life. That does not mean three is a magical number. It doesn't mean it's a sign. If you go around living your life based off of the way God works in other peoples lives then you aren't living the life God meant for you. You're not following God's lead for you. You're not following God's formula (by the way, there isn't one). You are just desperate for an answer and figure if it worked for one person then that must be the way to do it. Wrong.
God has a plan for YOUR life. And that plan has nothing to do with the plan He had for anyone else. Stop applying things that have nothing at all to do with you, or with how God works in your life, to your life. Find out how God wants to work in your life.
And guess what? Not moving on isn't a sign from God. It's a sign that you are clinging on to something that isn't going to happen. Just because you emotionally sit stagnant and dwell on someone doesn't mean anything spiritual. I was engaged at 20. For 20 years i haven't stopped thinking about her. But i know, now, that it would not have been a good idea to marry her. That doesn't mean anything spiritual.
You aren't moving on because you're holding on. Stop holding on and you can move on easier. Maybe there will always be a little part of him that sticks with you, but humans make connections. Doesn't mean it's from God, it means you're a normal human.
And as much as you're going to hate hearing it, at your age the chances of anything long term coming out of this are very slim. Yes, it does happen, but it's rare. And you haven't actually heard God tell you anything, you just assume it's God and look for reasons to validate holding on.