I can see why you would want to warn her, but she won't believe you. It is best that you just let her find out for herself because she will eventually.
how do you know if your boyfriend has cheated
Sounds like you need a better boyfriend.
Next Boyfriend....
tell her that her boyfriend cheated on her. she needs to know.
Dump him
you go and tell him you cheated on him and tell him how sorry you are and ask him to forgive you.
There is no way to positively know if your boyfriend has cheated on you unless you catch him or he tells you. There may be some signs such as not being where he says he is or lying to you on who he was with.
break up with him
yes. Why...?
her boyfriend cheated on her ;(
I do not have a boyfriend !! I know the longest relationship I had was 7 years! He cheated on me :(
No. He cheated and dies.