She's being intimidated. You can't do anything except to stand
strongly by her. She will have to stand up against the advances of
this guy by herself... If you interfere it would turn into a more
messy situation and your GF may end up hating you for it. This guy
probably experienced a broken relationship and is telling your GF
all about it.. Your GF's most probably a nice and kind girl.. Who
listens attentively, take cares of all her friends.. blar blar..
Give her time anyway.. If you are really that persistent in trying
to know what happen, ask her good friends lor.
Oh well.. Whatever happens, Stay firm! Do not
weaken!
Good
luck!~