Whats happening in Greys Anatomy???

I use to watch the show religiously, but I missed the first few episodes this season and then just stopped watching it. I saw an episode tonight and have no idea what is going on! Who was derrick shepard kissing?? If anyone could update me on what is going on with izzy, george, yang, the new interns (I have no idea how many they are, I just know that one that is merediths sister) and most of all, what is going on with meredith and derrick??! if anything?? After this episode it looks like nothing is happening with them, but does it seem like it will at all?

When I asked about what is happening with derrick kissing that woman, he was kissing someone who was in the ER with him..like a fellow doctor or something...im just curious about that..and tonight meredith said that she dosent want him seeing other people. But he seemed like he liked kissing that chick in the ER. So whats up with that

Izzy and George ARE together now, he told her the next time he gets married he wants it to last forever
Yang is trying to get in the good graces of the head cardio surg.
Seems like Izzy is questioning whether or not she is right for Cardio, or needs to do something more patient based
Meredith told McDreamy that she didn't want him to date anyone else...that she was trying ....this all happen after he kissed an intern after a really stressful surgery in which she saved the day, but nothing else has come from that kiss..yet
Meredith's half sister is trying to be friends with her, but she wasn't having it....then Yang brought her home to party with them after everyone had a rough day and it looked like meredith was going to accept it.
Dr. Bailey has replaced george's ex-wife (can't remember her name) as the head person. but now her relationship with her husband is on the rocks.

-izzy and george got back together and then broke up again.
-yang and burk are not together burk left the hospital
-meredith and mcdreamy are having "break up sex"
-yang is being pushed out of cardio kinda by the new head person in cardio so she's really trying to fight for that but izzy thinks that she wants that
-merediths sister and alex are sorta messing around
-Derrick was kissing some chick he met at a bar (I think)

I cant really remember much else at the moment. Hope this helps.