There are lot of different relationships on Grey's Anatomy. Can you keep them all straight? Here's a rundown.
Meredith sleeps with Derek before she realizes that he is her boss. In the beginning of season 1 she thwarts his advances, but finally gives in. For awhile they keep their relationship a secret, but it's not too long until the whole hospital knows. By the middle of season 1, they are no longer keeping it secret. But at the end of season 1, Derek's wife shows up and the Derek/Meredith thing is over (for now).
In season 2, Meredith takes a guy home that she meets at Joe's. The next day, he needs to be seen at the hospital for his constant erection and Derek finds out that Meredith had slept with him. Meredith is embarrassed and Derek is hurt.
Meredith begins dating the vet of her and Derek's shared dog, Doc. Derek realizes that he doesn't love Addison and doesn't want to be with her, but allows Meredith time to make her choice between him and Finn.
Meredith finally chooses Derek, but then he says he needs time to get over the fact that Addison had a relationship with Mark.
Meredith and Derek do end up back together, but then break up when Meredith can't commit. They continue having sex, until Derek starts dating a nurse, Rose. Meredith and Derek realize they belong together after working closely together and finally succeeding with a clinic trial. Meredith reluctantly asks Derek to move in, which he does, but Meredith will not kick out her roommates, Izzie and Alex.
They decide to get married, but give up their wedding so that Izzie and Alex can get married. They end up writing promises to each other on a Post-It Note and consider themselves married.
Preston Burke notices Cristina and brings her coffee. She is surprised by this, but later when she walks in on him while he is changing, they hook up. Their relationship continues in secret throughout season 1. Cristina discovers she is pregnant, but doesn't share this information and schedules a D&C. In season 2, Cristina loses the baby and Burke finds out about the pregnancy. They get back together and Burke tells Chief Webber of their relationship.
Cristina has trouble coping with the fact that Burke may no longer be a great surgeon after he is shot. She comes up with a scheme so that Burke can operate without anyone knowing he has tremors in his hand. She is extremely upset when he asks her to step away from a surgery and tells the chief what is going on. Derek is able to fix Burke's hand.
He asks Cristina to marry him and she says yes, but he leaves her at the altar. Cristina is devastated and doesn't date again until Owen Hunt comes to Seattle Grace in season 5.
Owen was a major in the Army and is a trauma surgeon. He and Cristina begin dating, but break up after Owen chokes Cristina in his sleep, but as he goes through therapy, she gets back together with him. They have a rocky relationship because Owen seems to be in love with both Cristina and Teddy Altman. He chooses Cristina, though.
Izzie begins to show interest in Alex at the beginning of season 2. He takes her out on a date, but she has a horrible time. He doesn't even kiss her good night. She complains to George, and the next day Alex kisses her. Izzie thinks they have a relationship until she catches him in bed with George's ex-girlfriend, Olivia.
Izzie eventually forgives Alex and they continue dating until Izzie falls in love with Denny Dequette.
Denny is a patient of Burke's waiting for a new heart. Izzie cuts Denny's LVAD wire so that he will move up the donor list and get a heart. The surgery is successful, but Denny dies a couple of days later after proposing to Izzie.
Denny leaves Izzie 8.7 million dollars. Much to George's distress, she keeps the check under a magnet on the refrigerator, waiting until she thinks of something spectacular to do with it. When Bailey speaks of her idea to open a free clinic, Izzie invests her money into it.
A long time after Denny's death, Izzie begins dating Alex again, but she starts seeing Denny everywhere and even carries on a relationship with him, though she knows that he is dead. Once she realizes that it's cancer causing her to hallucinate, Izzie looks to Alex, and when she is at her sickest, they get married.
When she starts to get better, she distances herself from Alex and leaves for awhile. She comes back and wants him back, but he says he deserves to be treated better than how she treats him. She leaves again.
Izzie begins to show interest in Alex at the beginning of season 2. He takes her out on a date, but seems distant. After hearing the complaints that he didn't even kiss her good night, he kisses her in Joe's bar. Alex has performance anxiety when he is with Izzie and ends up sleeping with Olivia, but Izzie catches him.
Izzie eventually forgives him and they begin dating again, until Alex notices how close she is getting to a patient. After Denny's death, Alex carries Izzie away.
A while after Denny's death, they begin dating again. Alex feels her pulling away, but won't break up with her.
When Izzie is really sick and it looks like she is going to die, Alex marries her. When Izzie starts to get better, the two find it hard to fall into a normal relationship and Izzie leaves.
Alex begins sleeping with Lexie and they soon begin a real relationship.