Could be nothing, could be something. I had something similar happen where she went of and danced with other guys and this led to her flirting with them. Usually I wouldn't give a shit because I'm not a big fan of being jealous, but in this case it was a bit too much I think.
I talked to the girl about it when we both weren't drunk anymore about how it made me feel a bit uncomfortable and during that conversation she broke up with me because she hadn't been feeling us together anymore. To be fair, we were only together for five months, not two years like you.
So yeah, might be nothing, might be something. Just talk to her and see where you stand.