I'm thinking of infiltrating the chat.
Which chat are you going to barge in on?
I'm thinking about infiltrating into the chatroom of my girlfriend's friends to find out her secrets.
Chatrooms are invitation only. You going into your gf's friend's chat to get the dish on her is incorrect. Show some respect and stay out of places you are not invited.
They don't respect me so why should I respect them?
Even if you don't respect them, you need to respect your girlfriend's privacy. Just let them have their group chat.