I agree with you both Vildis and sjhubby, why would Stella suddenly demand from Mac to choose between her and Ms. Doc when there was never any indication that she had more feelings for him than just a good platonic friendship? They cannot suddenly change her into the "madly in love with Mac"-Stella, that would be ridiculous.
And it´s true, Adam has changed a lot in this season, and I think Stella is playing a big part in this. Also I agree that maybe they were still seeing each other after that night, because there were some scenes where I felt that Stella deliberately tried to be more distant toward Adam in the lab, as if she was afraid that someone might take notice of their relationship.