I can never resist answering a "dream analysis" question :)
I have very detailed dreams and I often reflect on their meaning, even kept a "dream journal" for several years, which really helped me start to figure them out.
I agree with what osohapi found on "dreammoods (never heard of it, I
ll have to check it out!), and also Theresa. It is more about what that time represents, and about who you were at that time. I often dream about my ex from when I was 19/20. That is such a ripe age for self discovery, and there is a lot of personal growth that goes on during your first "real" relationship. It is probably more about that.
I also often dream of a faceless "new relationship" I am just starting out, and I am usually around that same age, 19/20. Then the dream morphs and I realize I am a grown-up with a husband and kids. I think I dream that because it is feeling that can never be duplicated again once you are old and married, so I get "re-experience" it in my subconscious now and again, which is nice. So your dream could also be about that, trying to experience something you don't have anymore (not in a bad way, in my case I feel very happy with my current state of life, and husband, so I never feel bummed out or anything when I wake up).
Personally, I see nothing wrong with looking up old flames on Facebook or whatever. I think it's nice to see people who were important from your past and what has become of them. I also disagree with people who feel good about seeing their exes get fat or bald. Or feeling happy that they dodged a bullet (no offense B and mommyof1). I am in touch with both my exes on FB and occasionally an email. Whenever I see pictures of them I think they still look great and I wanna pat myself on the back for picking out such handsome dudes. And they both seem to have healthy relationships with nice-looking wives, one has a a super cute kid, they enjoy and are successful in their careers. I think I could have been perfectly happy married to either one of them. So no bullet dodging there :) Does this mean I have any issues with my own relationship? Nope, my life path led me to another great guy and I am very happy married to him. Like you, I no longer have feelings for them, other than a great fondness. I hope my exes think the same way about me!
I think you should look him up (since you seem to have a healthy view of your past relationship and are happy in your current one).
Only you know why he popped into your dream out of nowhere, and maybe reading this thread will help you identify that (and most of us are saying it seems to have nothing to do with your feelings toward HIM, more about your feelings about yourself, when you were dating him.
PS don't be surprised if he comes into your dreams more often now that you are reflecting on it :)