While Grey's Anatomy's season 17 finale ended with a hopeful note for the future, there was no happy ending for Link as Amelia turned down his long-planned proposal. But why did she reject Link despite them having a child together and seemingly being happily in love? The signs have been there as the season has gone on, so the twist should only have come as a shock to Link himself.
Link and Amelia's relationship has had its fraught moments, particularly when there was uncertainty over the true identity of her son Scout's father for a while. That saw Link almost end the relationship as he wrestled with the prospect of raising Owen Hunt's son. But then, as a mark of Grey's Anatomy's progression away from every dark outcome, Link was revealed to be Scout's biological father and he again realized why he'd turned down his dream job opportunity not so long ago to be with Amelia.
Sadly, Link making that decision was never going to be an indication of a perfect relationship or an assurance of their happily ever after. After all, Link was always something of a nomad and was reluctant when the idea of traditional stable relationships came up and Amelia wears the scars of her past trauma - emotional, medical, psychological, and personal - very close to the surface. She has told Link she was a terrible wife to Owen Hunt, dismissing the excuse that she had a personality-changing brain tumor at the time, and elsewhere in season 17 she told Link somewhat dismissively that she hadn't even had time to think about marriage. The finale doubled down on Amelia's feelings, having her realize through her therapy zoom group that she simply didn't want what Link wants. No marriage, no more children, no conventional relationship set-up, and presumably no Link now as a result, given he ends up at Jo's new apartment. And it's not just that Amelia doesn't want a marriage that's important here, it's that she allowed her feelings to dictate what she wanted, in defiance of her historically self-destructive impulses, and though it's devastating to Link, this all represents growth for Amelia.
Amelia is an addict and always will be, whether she's in recovery or not. She's also been forced throughout season 17 into the housewife with multiple kids role because of Meredith's illness and her availability as childcare. The old Amelia would probably have toed the line, believing that the pretense of a perfect family life and relationship could fill the hole in her, which would have exacerbated her issues and led to more self-destructive problems in the future. In fact, the old Grey's Anatomy would have let the couple marry and end up on the ever-growing trash-pile of failed marriages and relationships that have punctuated its long run-time, so this catastrophic end for Link represents growth for both parties. In hurting Link, Amelia has found some healing in herself.
There is, of course, the possibility that the couple will get back together in Season 18 of Grey's Anatomy - even if the trajectory of Link's arc seems to be pushing him towards Jo Wilson - but it cannot be at the expense of Amelia's self-care. Because as Richard pointed out to her in her therapy pep talk, it is wrong to assume that addiction is the only thing wrong in an addict's life, and Amelia recognizing the fact should not be walked back. All that lies down that path is another relationship on Grey's Anatomy where one party loves the other adoringly and the other loses sleep wondering how to get out of there. And Link doesn't deserve that and Amelia doesn't deserve to be painted as that villain cliche. It's been done on this show already too many times.