My boyfriend is talking to this girl behind my back?

SoulGirl
Okay so I know that if my boyfriend talks to girls it's completely normal. I agree , and he has some girl best friends too that he has mentioned before so I trust him with that. We've been going out for 4 months. but now I've been seeing that my boyfriend is now talking to this girl that he has never mentioned before.

In the summer time, I noticed my bf's friend got in a relationship with this girl. Then about 1-2 days later my boyfriends' friend dumped her.

Then all I can see is the girl writing on my boyfriend's wall and telling each other to message on msn. I'm not sure who added who. I also caught him telling her how it sucked that her phone was broken and that they couldn't text.

Then recently she got a new phone and immediately wrote on his wall about it, and told him how she did promise to text him first and telling him to text back.

The "FIRST" guy to text on her new phone is my bf? I think something is fishy.

And I do believe that they have never met up in person either... unless my boyfriend did without telling me... because my bf's friend only went out with her for 1-2 days.. and when he dumped her my boyfriend and the girl added each other on fb when or after she was dating my bf's friend, so I know they didn't know each other before. My boyfriend NEVER mentioned her to me before.

My boyfriend is also VERY protective of me. When I went to a party with him he was telling his friends to not let any guy talk to me and if a guy tries to get with me he will break his neck or whatever.

Should I be very concerned?
My boyfriend is talking to this girl behind my back?
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