I miss my first serious boyfriend from 10 years ago sometimes. We haven't spoken in ages and I know he's moved on but I feel like I'll always miss him though I don't even know who he is now.
That is a long time.  Do you still have contact with him in any way?
Yes, I'm friends with him on facebook.
I understand that it can be hard to move on from the past, especially previous relationships. However, it can be dangerous to never move on and to dwell so much on something that happened 10 years ago. Clinging to a previous relationship makes it harder for you to find new potential partners that would make you happy.
I've had a couple of relationships since but none of them were as good as that one.
10 years is a long time. I'm sure both of you have changed tremendously. It is best to try and move on so you can be happy.