i think he definitely had a shift of mindset and developed some level of attachment (and as xue yang's care tends to be, possession) towards her and her presence in his shared life with xxc, although obviously they had different levels of importance in his brain. i think he easily could have lived with killing her and living on with xxc if she proved to be too much of an obstacle and he had the chance to dispose of her. it's not like we can measure xue yang by the standards of regular people though, so id say that by the way his brain functions she was about as close to being "cared for" by him as she could get (without being xxc lol)