You can tell for sure that your girlfriend is cheating, by catching her on the act with her lover.
stalk her
Yes you should tell her that he is cheating. Because later, it will hurt her if not told.
One way to try to tell if your girlfriend is cheating is if she's refusing to spend time with you. If she has a new boyfriend she may want to spend less time with you.
tell her.
you can't. just have to trust her, dude.
There is no test to take that will tell you if your girlfriend is cheating on you are not. Girls all act differently and the fact is she is either cheating or not and no test can 100% tell you.
be as honest and sensitive as possible and make sure that you have proof that the person was cheating
Your girlfriend's cheating
You cannot tell absolutely except by catching them together.
ypu can tell your girlfriend is cheating when she dont act like she used to act she acts all suspicious.she begins to blame u for cheating wen she the one really cheating.
ask her and tell her not to lie or you could just breakup with her and move on.