can anyone tell me what happend in the seson finale? and also what happend to Robbie??

From TV Tome:
When Simon and his new girlfriend Rose (guest-star Sarah Thompson), make an unexpected visit to Glenoak to meet their respective parents, Annie begins to suspect their relationship might be on a fast track. She let's them know they are not allowed to sleep in the same room together in the house as they spend the night. Rose puts up a fight with both Annie and Simon over the sleeping arrangements, but eventually take will. Meanwhile, Eric hides the news of Mary's (Jessica Biel, who does not appear in the episode) divorce, worried that it will most certainly break Annie's heart. Also, Martin becomes the third wheel again in Ruthie and Vincent's relationship as Ruthie thinks Martin is jealous of their relationship despite the fact that Vincent wants Martin to convince Ruthie to dump him. The adoption process for George (guest-star Brad Maule) and his wife over the Davis children becomes more complicated when their biological mother fights for the adoption process to not happen. Lastly, Martin's father, Bill (guest-star Costas Mandylor) returns from Iraq to greet his son.

It was never really clear why Robbie left the show. For the show itself he moved down Florida to be with his mother. In real life I believe the actor Adam Lavorgna had problems (maybe drug related) and they got rid of him.

I don't even remeber what happend in it. I watched the episode but I wasn't paying that much attention to it. I remeber it being a boring episode.