<human>: Can you provide a brief overview of the text?

Hello!  
  
I have been together with my girlfriend for about a year now, and so far it has been going great. We know each other for more than that since we started out as roommates. Although we still haven't gone out of the closet, only a few close friends knows about our relationship.  
  
A few weeks ago she started chatting on skype with this guy, I noticed this because she is on her computer more. This morning, she left her computer on when she went out. I know I was wrong in trying to read, but the last bit of their conversation got me looking cause they were talking about how big his dick is and how my girlfriend wants to see it.  
  
So I tried to scroll up and read their past chats and I was really surprised that they mostly talk sexual. My gf has been showing him revealing photos of her, they talk about their sexual fantasies. My gf also has been telling him what we(me and her) do in bed. She is also very flirty and teasing him a lot, and even suggesting that she has been masturbating thinking of him. He is from Sweden and mentioned he might have some plans to come here and visit Tokyo.  
  
I acted normal when she came back home today, but I am really conflicted inside. I feel mad, jealous, betrayed, cheated. I know I should confront her, but I don't know if I am just over-reacting. Does chats like that considered cheating?  I also don't know how to confront her. :(
<bot>: I saw my gf's skype chat with a guy, and it is mostly sexual. I feel cheated, but I do not know If I am just over-reacting.