Yes. It is easier to tell a stranger then a friend. But only if you have hard facts. You don't want to cause trouble.
Second Answer- I think this should be answered both ways for the sake of being fair. If it's a stranger then I suggest you keep it that way. There may be circumstances that you don't know about. Such as an open relationship or the two weren't together at the time. Either way it's a stranger and therefore not your business to meddle in their affairs. ( Ha ha literally)
Addendum:There is a saying from the streets: "Snitches get stitches." It would be wise to consider the metaphorical and literal implications of this.
There is a reason that law enforcement does not like domestic dispute calls, you need to consider why you would want to insert yourself into one.
You should tell your friend that he is cheating its best that she knows.
Tell him the truth, say you like girls.
You should tell the other girl and both break up with your boyfriend.
Ask him :/
Explain The Circumstances (: She Should Understand. Afterall She Is Your Mom
No, she will find out eventually. IF you do tell, she might take it negatively and this might ruin your friendship.
You tell the truth and accept the consequences.
You would not like it if your best friend cheated on you with your boyfriend so that is not a nice thing to do to your best friend. First, you should stop saying you are best friends with the girl when you are 'cheating" with her boyfriend. Best friends do not do that. Second, you should stop going out with her boyfriend. Third, you should tell the girl that the guy is cheating on her, even though you will need to tell her that it is with you. If he does it with you, there is a real good chance that he would cheat on her with someone else. Finally, both of you should dump the guy.
You should tell him that you know that he's cheating on you and tell him how you feel about it. Also if he then goes hmmm... ok then just do the same back if your a bitch or if your nice then just dump them.
Tell him to come clean about it, or you will. Give him some time to do it himself, but if you don't hear anything about it then you should tell her yourself.
In most cases if a boyfriend was not cheating and was accused by his girlfriend then he would be angry and since your boyfriend is silent there is a high possibility he is cheating and cannot own up to it.
No. Blackmail would be if you went to the boyfriend and threatened to tell on him unless he paid you something.