Guys, it may not what you think. TPTB could fool you, make it look like Greg and Sara get in a fight. I don't think it got nothing to do about Sara marry Grissom. Next week, Sara and Grissom are marry now. Greg love her like a sister, Sara love him like a brother to her. Jorja said that in her interview 2 or 3 years ago.
I think Greg is hurt that Sara didn't trust him enough to tell him that she is marry to Grissom. I still can't picture Greg or Nick get in a fight with Sara. Catherine, yes, I do see between her and Sara get in a fight.