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 Amore and happy- until Addie showed up as Der's wife- which i believe has damaged Mer...