Wonderwall defined...

1
Some one who you find yourself thinking about all the time, the person who you are completely infatuated with. the one that you look for on your buddy list every time you sign online. the one who has a heart next to their name in your phone book. the person that you find yourself completely head over heals for.
2
Something or someone that is always interesting. For instance, when you lay in bed at night, you can stare at your wall and begin to notice all the little details that you wouldn't have notice otherwise. A wonderwall reflects your greatest thoughts and emotions.
3
(noun):
the person of which you have a total infatuation with;
a person with an indescribable aura, making them seem so perfect, almost intangible;
the person that you feel could be the one to "save you" from whatever unhappiness or emptiness you feel;
the person you feel could complete you;
your soul mate
4
The one you want to spend the rest of your life with, your only reason for life.

http://www.urbandictionary.com/define.php?term=wonderwall