I've had one & its happened a couple of times.
In elementary thru high school, there was a guy that was a very good close friend...though I wished it was more.

He was SOOOO popular with the girls....and I never understood why he had anything to do with me since I wasn't that popular. Anyway, he even went to my sr prom with me when my boyfriends mom wouldn't allow him to go.
We kept in touch after graduation by letters for a while while he traveled in the military. We then lost touch of each other.
Meantime, I'm in college & get engaged to someone. Engaged 3 yrs. 6 mths before wedding, I met someone at work. Wasn't looking. It just happened. Everyone at work (married ladies) are like, go out with him on a date, otherwise you'll never know. Long story short, 4 mths later (now 2 mths before the wedding), I decide I can't get married because I'm falling in love with this guy from work. I'm on my way to fiances apartment to break it off --- still VERY CONFUSED about if I'm doing the right thing (puking for months & loosing weight). I decide to stop at McD's were I used to work & were I haven't been in over a year.
Well, who's walking out of McD's while I'm walking in.....but the guy friend from high school. (Home on leave.) We hug..... talk for a LONG time about what I'm about to do. He tells me my fiance doesn't sound my type at all.....and the guy from work does.
OK, break off wedding......2 yrs later, marry guy from work (my DH) who also happens to be military.
Ok, YEARS & YEARS pass. My DH knows the story of high school friend going to prom with me & running into him at McD's that day. DH knows his name. DH has seen pictures of him. High school friend doesn't know DH's name....there was no reason to tell him when I saw him at McD's.
So, DH on vacation 1 day. We both stop into the armory where he works. All the men gathered around & everyone talking. As 1 man spoke from across the group, I just stared at him. Something about him was SOOOO familiar -- his eyes. Yet, he had an accent & I couldn't read his name on uniform. Group breaks up & I ask DH what that man's name was. He says the last name (after all, that's all how they address each other). OMG, could it be? Its my high school friend. I say the first name...and he's not sure. I smack DH & say.... "you've been working with XXXX & you didn't even know it?". I go back & find high school friend. It had been so long, he wasn't sure it was me in the group talking & I didn't recogonize him at first. He had been stationed all over the world....and here he was stationed near us now. Just Amazing.
I often have dreams that he ends up in one way or another. When I awake, I realize what date it is..and its usually a date of importance.
I think he is somehow my guardian angel. Making sure I didn't marry the wrong guy. And just keeps re-appearing in my life when appropriate.
We keep loosing touch. But we keep finding each other. Recently connected again on classmates.com.
Mind you....all these occurances happened all over the state of MA & RI...not simply in our hometown. Even weirder.