Your friend should really do more communication with her bf...
It's really hard to just spectaculate this way or not rather
meaningless...?
Possible reasons mostly have been mentioned, except if if her bf is
quitte a mature one, he might be having problems with issue(s) of
other concern in his life....
If she's afraid to face him, there won't be much we can do about it
too...
Btw, you really seems reluctant to reveal much more details
yeah...? 
