Is it normal to think you want your 1st love even though you never see them?

I'm sorry this is so long but could use some answers from anybody that understands, if you don't feel like reading it then don't, but move on and don't bash.

So there was this girl I use to go out with when I was about 14 and 15 and she was my first real girlfriend. We were really in love, I mean really. I live in a subdivision and we made out in every section and on every square foot of that place haha. I broke up with HER because I being immiture thought it would be a fun game or something to play. She moved away not long after and we never got the chance to patch things up. I'm 24 years old now and all through out my life she always popped up in my head. Just random thoughts of her ALL OF THE TIME! I have had so many serious relationships since, even an engagement. I've thought about other ex girlfriends but she is the ONE girl that always remained constant in my mind and I never stopped thinking about her once and I don't know why. I always just wanted to come out and tell her all of this but I am too certain she would be like "What the! that's weird i don't even know you anymore" I ran in to her 4 or 5 times since and it always seemed like she would show up right after I was thinking about her. One time she even ended up in a course I was taking. She even talked to me online once or twice or visa versa when we were'nt feeling to akward towards each other. She said something like "I use to be so inlove with you" or something one time and then ended the convo quickly after. Maybe her bf was there. Anyway 4 or 5 yrs go by without having ANY contact with her and I still always think about this girl, she was adorable and still is. I always thought she was the most beautiful girl I ever seen and I'm not saying that as a cleshay I mean it. I don't know what to do and I can't believe not only do I always think about her still but I get actually depressed sometimes. She's the last real memory when I can remember being happy and not having a care in the world. btw she's engaged and not the type to cheat. From what I hear she loves him alot. I'm not asking if you still think about your first love, I know alot of people have that problem. Has anybody ever obsessed to this degree about a girl they never talked to in 5 years and know there is probably no chance in ever being with her?