Gosh you missed a TON! They've bene having a relationship on the down low for a couple YEARS. The minature killer abducted Sara and stuck her under a car in a desert and that's when Grissom lost it and just outed the relationship and wigged out trying to find her.
They found her, and Grissom proposed when she was up and around again...I think I missed one after than...but Sara's been falling apart by slow degrees as to her job satisfaction...being more sensitive and hormonal, etc.