I prefer to see allience between Gortash and the Dark Urge not as something recent but as a partnership that started more than ten years ago. And it took long and careful dance of courtship for them to start getting closer.
It took Gortash asking several times for the Dark Urge to stay a bit longer and to share a glass of wine and the Dark Urge very slowly starts setting precedents for more and more proximity as one day they are willing to step out of shadows and stand a bit closer to Gortash and then maybe they are willing to stay a bit longer and exchange few words not relayed to their allience and then maybe they are willing to even sit down and so on...
I'm really fond of the idea of them growing closer just very slowly and teasing and testing each other. And looking back neither of them can really pinpoint one single moment when they started to be important to one another, when they truly started to care.
It was all just series of many insignificant moments piling up that grew into genuine mutual affection.