There are a few common signs for cheating, I have added a link to a video with the 10 most common ones, :)
tell her that her boyfriend cheated on her. she needs to know.
how do you know if your boyfriend has cheated
you go and tell him you cheated on him and tell him how sorry you are and ask him to forgive you.
Are you the person they were cheating or was it someone else? If someone was cheating you, I would say I didn't want to be their girlfriend (or boyfriend if you are a guy) anymore and that I saw them cheating. If it is someone else that was being cheated, I would tell the person who is being cheated and tell the person what I saw the person do.
not unless you are supposedly a virgin and you have sex with him. or if your friend tells him. those are the only two surefire ways to know when someone has cheated but if not by those ways and if u dont tell him then no he wont know.
tell him you cheated on him
kiss them
He will tell you.. men never lie.
They may be jealous... Or hate you. Either way, tell him its not true.
You guys need to talk about this and consider your options. Goood Luck!
Tell him honestly & as soon as possible. Don't omit information, either. You were reckless. Since you cheated, face the consequences.
Lie and tell him you cheated on him... he'll tell you just to get even with you.