Did i overreact at my boyfriend?:(?

I've been with my boyfriend,Ross for about 3 months now and from what i heard from my best friends boyfriend(Mark) my boyfriend was seen with this girl(Emily) who has a reputation for cheating and stealing boyfriends,was going off alone with Ross and they've been getting really close..she's easy to fall for since shes pretty and really flirty she has a boyfriend but she still isn't afraid of cheating or flirting around him...i ended up yelling at my boyfriend with him denying it and i asked his ex(Leanne) which is best friends with Emily she said she saw nothing suspicious but they were really close last week they all go to a different school from me I'm just worried becos Emily actually does flirt with every boy she speaks with:/ Ross got offended when I said i don't like her much...