I'd look into the entire dialouge for that scene & not just the one line. Ryan asks who the guy is with Calleigh (It's Terrance the horeguy [last epi] for those who don't know)- when Eric says who he is, he comments that the guy
better treat her right.
Now think about it....if two people are "together" then the guy is not going to say that another man better treat her right!
I do believe there's something ambiguos about his line "Yeah, Im her guy". Ya have to consider how it comes off on screen & not how it comes off on paper (if it even get's to the screen) - the tone in how they say these things are very telling...it could very well be that he is saying it with disbelief (as in "yeah, right") or he just thinks that.
Given that he's viewing a photo of her with another man & saying that this "new man" better treat her right, in my opinion Eric thinks she has moved on. Don't let the spoilers fool ya.