Sometimes I wake up in the middle of the night wondering what his reason for breaking up over a letter cud be ....
And then I have to tell myself ..its fiction, its a sitcom ....
But, seriously, even fanfic somehow has mostly not answered that question ...i read one fanfic that was written years ago , which mite be the only one that tried addressing why an in character eric may have written that letter,,,,the story goes onto say that he was in a situation where there was some serious riots or terrorist attacks or something of that sort going on ...and he didn't want donna to live forever just with his memory if something happened to him ....so it went kinda like he wanted to set her free to move on before something happened to him. :-(
stupid S7 and S8writers....