it depends how well and how long they have known each other. You should first think to trust your girlfriend no matter what, but if they haven't known each other for that long, there is probably something wrong. If they are not that well of friends, or are just "friends" then I would say there is something wrong, and it is weird that she did not ask you.
Ulterior motives are hidden or undisclosed reasons for someone's actions or behavior that are different from the reasons they claim. These motives are typically self-serving and may not align with the overt intentions being expressed.
Example sentence - It soon became clear he had ulterior motives in regards to her future.
Anybody can add any body on Facebook, provided there are not ulterior motives in doing so. People hide under the guise of Facebook friends to commit crimes. Such attitude can lead to separation and destroy the friendship.
The likely word is ulterior (concealed or hidden, notably motives or impetus).
Friends who talk behind your back have ulterior motives. They don't want you to be successful and win in life.
Abstract Underwraps - 2013 Ulterior Motives Part 1 1-1 was released on: USA: 16 January 2013
Abstract Underwraps - 2013 Ulterior Motives Part 2 1-2 was released on: USA: 23 January 2013
Funerals are generally open to anyone wishing to attend; that is the tradition. Perhaps this ex girlfriend will make a false display of grief, and has ulterior motives for attending, but I suggest that you just ignore her.
Motives can be good or bad, open or ulterior, simple or complex, strong or weak, sane or insane.
Philip Spector, until she catches on to his Ulterior motives.
Usually, when a girl just wants to be friends with someone, they just want to be friends. Girls never have ulterior motives behind their actions. And being in a relationship is trusting the other person, so you do nothing.
William Pickering was behind the Deception because he had ulterior motives and wanted to destroy the Senator's campaign.