Contacts Group Code

Hello, i posted this thread here because i'm using WPF technology, so i'll explain my problem.

I'm developing a group system for managing contacts, the system is done, i just feel the way i'm doing it is not the most efficient one, so i'll explain how i'm doing it:

When the application loads up, it searches for files with extension ".cp", which i gave to the files, those files contain the contacts stored before closing the application, the applications uses a default contacts group named "Contacts" which will hold all the contacts that are not set to a group, so the applications creates new groups based on the name of the files that were found, the groups created contains the contacts in those files, the application saves by default 1 file, named Contacts, if you change the name of that file externally, then a group with that filename will be created, and if no file with the name "Contacts.cp" is found the default group for storing contacts is created.
here's a little chart on how my system works:

http://qmftsa.bay.livefilestore.com/...Iw/Imagen1.png

My point is, i'm i doing this the right way, or should i re-design the whole thing ? what i'm doing wrong? can someone show me the right way to do this ?

I'm a 14 years old teen, this is my first project i'm trying to follow a designing and developing process, being really organized so i would really like to get help on this one.

Also, how can i get all the contacts from the groups without having to create another group containing all the contacts in the other groups ?

Do the contact groups have to be stored in separate files? I mean was that a choice you made when thinking about how the app should be used or was that just something that you did purely to aid this grouping situation (ie, being able to determine what groups exist etc) ?

Well, since my application can import, export, contacts i found it helpful, for example you have a contacts group that has all the contacts from your work, and someone would like to have those contacts too, then you simply give him or her, the file containing the contacts from work, instead of he or she having all of your contacts, but that's just an option, the user can save their contacts in only one file.

So what do you do if a contact is in more than one group? Are they duplicated in each of the group files? Or do you not allow them to be assigned to more than one group

That would be an issue of the user, that will depend on how the user wants to administrate his contacts.

I've done a little example of the groups system, it's attached to this post, please try it, and let me know what you think about the app architecture, and if you sere something wrong or something that has to be imporved please let me know.

After thinking for a while, i came up with simplifying the whole thing, now the application only creates 1 file, the groups created by the user are located within that file also the contacts, so when the user wants to export only a group it will be easier to do, so i came up with this flow, for managing the groups, and the contacts within them.
http://qmftsa.bay.livefilestore.com/...jg/Imagen1.png
Still if someone has tips, or comments on this please post