Okay well this is the first time I did a soapbox, so yeah... and cuz i wrote too much English essays at school, u might find this very 'essay-ish' and formal, but i'll try to prevent doing that.
Okay now, Merder is my favourite couple on Grey's Anatomy, they're cute and sweet together, but how come they can't be together and have a stable relationship???
I think there're many reasons to explain this. Like for example, at the start of the series when they just met and Derek was chasing Mer, they seems soo in love and happy- until Addie showed up as Der's wife- which i believe has damaged Mer very deeply on the inside, and that's probably why Mer's finding it very hard to trust him again. Then, Derek 'moved on' with Addie and it took Mer a while to finally get over him and date Finn, however when the MerFinn relationship was just about to start, Der found out- which he wasn't very happy about because that means Mer has moved on without him. So he called her a whore- and that was very damaging to her as well because REALLY, she didn't do anything wrong that deserved to be called a whore.
This 'whore' thing showed that Der still has feeling for Mer and he want her to come back to him. So they had sex in the exam room (which I'm sure everyone has seen it czu it's a famous scene) So Mer got herself into a love triangle, which showed that she's not completely over Der yet, eventhough she's dating other poeple. She picked Derek (the right decision), but I'm not sure whether she picked him because she really REALLY loves him- since Finn is a very nice guy and Mer knew it herself that Finn wouldn't hurt her the way Derek did. So this might be something that's causing the trouble.
So they got together, happy and 'sexy'. Until a load of events started happening. First was Cristina/Burke thing, and that affected Merder's relationship a little because they're bothe great friends with them. And then Ellis Grey came into the picture and said some cruel and mean stuff to Mer which hurt her a lot and she became 'super deark and twisty'- that she nearly drowned. The drowning scene was a main focus for the merder relationship- first Mer didn't wanna live, so she didn't fight for her life, then Derek pulled her out from the water and brought her back to life. When chief and Bailey...ect. were helping to resuscitate Mer, it made Der doubt Mer.(which is not good)
Afterwards, Thatcher and the other mum came and changed Mer as well, Thatcher even slapped Mer because she couldn't save his wife. Mer got soooo extremely dark and twisty and Derek was trying to help her, but she wasn't letting him in. She turned herself to her friends instead and totally forgot about Derek, and that hurt Derek. Derek couldn't stand the ignorance from Mer and he turned himself to someone else (flirted with Lexie), and yet Mer still didn't see what she was suppose to do to keep Derek aroud. So that's why they broke up and the finale of season 3.
Season 4 started with them breaking up and 'break-up sexing'. So from this, we can see that they still feel each other and who cares if they're not together, doesn't mean they can't have sex!!LOL yeah anyway, but through all the sex and stuff she had with Der, she started to grow back her feeling for Der, and it's stronger. But the thing is, she doen't have the guts to tell him that, so Derek obviously doesn't feel it and found the most annoying person- Rose and asked her out. Mer, of course cannot blame Derek for what he did because he was just dating other ppl like a normal man would do. Mer got all pissed off so she went into therapy. Therapy lady was PRO cuz she can pointout wat exactly Mer needs and wat she's doing right now.
Derek on the otherhand, didn't quite get over Mer (well they never will actually ACTUALLY get over eachother), Rose to him is just like another refreshing woman- all new and fun, but his true love is still Mer. The clinical trial thing created a stronger bond between them and finally, FINALLY they saw wat they really want and get back together. I really hope the all 'breaking-up, getting-back together' thing stops because it would kill audiences.
hahahh~ okay i wrote too much, this is probably like a 800+ word essay...oopps. anyway, to conclude- I just hope that they can really see what they want/need and really go for it, because the relationship is not going to work out if they don't take it seriously. and they should take it seriously cuz separating is not doing any good for them.