Apparently US Weekly's report about Justin Timberlake sleeping with Olivia Munn came from a friend of Olivia. You can tell because it says things like, Munn resisted Justin's advances and kept telling him no because he was still with Jessica Biel. If it had come from somewhere else it would not have been that concerned about how Olivia looks in all of this. Anyway, the pair met at some MySpace event and the next thing you know they spent three days having sex and Justin lied to Olivia about being with Jessica and she thought Justin was the one and they were going to have a future together and that is the only reason she had sex with him for three straight days and blah blah blah.
If Jessica was upset it is probably just because she could not be there. Justin's rep denied it like crazy, but probably does not know. Olivia does not have a rep and does not comment on her personal life. Well, unless she is getting paid.