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When people ask Derek and Addison why they didn’t work out, the whole “cheating on Derek with his best friend” thing is usually enough explanation.
But their issues started long before that. How could they not when Addison was a fairytale heroine from another dimension whose only introduction to humanity was Derek and his daughter?
Turns out, having a romantic relationship with the second guy you’ve ever met doesn’t bode well for relationships and neither does falling for the manic pixie princess who makes you rediscover whimsy and passion while you’ve been in a loveless relationship for years.
Really, Nancy was so much more understanding than she should have been.
So, once their initial communication issues became detrimental to their relationship plus, with Addison realizing that their world had so much more to offer than Andalasian, she put aside her fashion career and pursued the medical field, specifically obsterics and gynecology, wanting to know everything about her own body and bodies like her.
Derek followed her lead and switched to the medical field, wanting to help people and fascinated by the human brain.
Their marriage was rough. With Derek coming out of his failed relationship with Nancy plus never truly getting over his first wife leaving him and Morgan, he didn’t exactly have the best track record.
Giselle on the other hand had no guage at all of what relationships were supposed to be like (besides getting married the day after you meet each other) and when she started to know more about the world, she grew more cynical about their relationship, realizing how flawed of a man Derek is and how incompatible they are in the long term.
He was the right someone to introduce her to this world but he was not the right person to stay with forever.
The first time she cheats on Derek, it’s before she really understands the gravity of cheating. She just understood that she had too much love to be contained in just herself and for Derek. When she realized the severity of what she had done, she knew she could never tell Derek, in fear of losing him even though they had been losing each other slowly.
When things were clear that they weren’t going to mend on their own, she just… she needed more. She needed to learn. She needed to learn what love actually was. And she couldn’t do that while tethered to Derek.
Derek on the other hand had been working hard on being a better man for his daughter if not for himself.
Addison would always love Morgan like her own, but she didn’t fully fathom what parenthood required and as Morgan got older, Derek needed her to shoulder more responsibility than she was capable of holding.
They were estranged for a while. Together enough to not make things too rocky for Morgan.
Derek knew the signs. He had been a divorce lawyer for fucks sake. He knew that they needed to get a divorce.
But he had never been good at admitting to himself that whatever reasons he convinced himself was enough to stay could never be enough.
He had done it to Nancy, stringing her along for far too long, unable to commit in the way she deserved. The end of his first marriage was forced upon on him when she decided to leave.
He doesn’t know how to end things that he thinks can get better.
Which is how they somehow are together for eleven years.
Morgan, now seventeen, has contemptment towards her stepmother, but also a fierce love for her the more Addison had learned about the world and evolved as a person.
It had always been messy but finding Addison with Mark was the final straw. Of course he knew about her many partners along the years. They hadn’t truly been together since they first met. He knew that he was not hers.
But for her to bring it into their home. For her to bring his best friend into his bedroom in his home just down the hall from where their daughter slept.
They could never recover from that.
With Morgan in college, there was no more flimsy reasons to stay together anymore to give her stability (which they hadn’t been giving her in the first place).
So Derek left New York to Seattle to finally get a new start.
When Derek meets Meredith Grey, when he falls for her, he tries to stop himself. She doesn’t deserve to be what Addison had been to him, a distraction from a failed relationship, and idea of a partner.
Yet he can’t stop himself from pursuing her. There’s something different about her. Something…
Something he never felt with any of the women he had been with.
At first, it’s nice to hide behind the blanket of anonymity with her, but he knows she needs to know the truth.
So he lies it out for her. His life is messy. He’s got an eighteen year old daughter off at college. He was married young to a woman who left him and their baby. He dated another woman for five years before they split and he got married to Addison for 11 years.
It’s… a lot. Especially for the young 25 year old, thirteen years younger than him but with such a vast canyon of differing life experience.
But it doesn’t scare her away, somehow, even though it should have.
Meredith Grey gives him a chance. Just with the promise that he is completely honest with her.
So he is.
Well.
As honest as he can be.
Because there is one thing he hasn’t been fully honest with her about, and that involves magical kingdoms, transdimensional sewers, and evil witches that turn into dragons.