My best friend of like forever and I split up and I don't even know why.. 15 years gone with no heart?

People change and sometimes people grow apart. Jen has changed and she has a lot of other friends besides you and apparently she feels she has more in common with them. Or something like that. Why not send her the card and see if she writes back? She may be thinking about you too but just doesn't know what to say. Or the friendship may be over. It is better to know for sure. Then you can grieve, accept it and then move on.