I got this idea while listening to a german song:
Alex Whitman is new in town and immediately after moving into his new appartement, he falls in love with his gorgeous next door neighbor Isabel Evans.
Sadly, he's too shy to talk to her (maybe being quite insecure about himself) and so they never get to know each other and Alex suffers from watching Isabel go on dates (with her boyfriend or various guys).
One day they get to talk (while doing the laundry or something) and Isabel confesses that she's tired of those idiots who don't want to get to know her and only want to get her into bed, etc.
Alex finally gets the courage to ask her out but when he wants to ask her (with flowers and all), he sees her going out on a date with yet another moron.
Later that night, he hears some havoc in Isabel's appartement and curiosity gets the better of him. He spots a bulgar in there who already knocked Isabel out while her date is sitting in a corner scared.
Trying to stop the bulgar, Alex gets knocked out too but the bulgar does leave. When Alex wakes up again, he learns that Isabel's date told her he was the one who saved both Isabel and Alex.
Isabel is of course impressed and Alex really devasted about Isabel believing the guy and now going steady with him. Because of this, he moves out because he can't stand to see Isabel with that guy (yes, sounds kinda wimpy).
Somehow, Isabel (of course) finds out that her boyfriend lied and it was Alex who saved her. Thinking back she realized that Alex was always nice, kind, etc. to her and when she goes over to thank him, she learns that he moved out.
Now, Isabel is the one woh's devated because she suddenly realized that she cared for Alex.
Well, you can either stop here - leaving with a sad end. Or you can have A/I meet again - either because Isabel looked for him or they accidently meet at the dentist or somewhere.
I'd prefer the happy ending

and ... please, DON'T get graphic about Isabel dating the other guys!!!!! That's very important.
Otherwise, have fun writing!
