“I must accept that Louis had become the brilliant star for Merrick, and by that light I shone no more.”
The relationship between these two is mostly from when they were mortal. David was Merrick’s savior and Merrick was the only woman that David was ever in love with. Merrick harbors a great love for David but David seems to doubt it because she falls for Louis. Though Merrick is much younger than David they both see beyond that, and David sees beyond his prominent homosexuality. Their relationship is only described in Merrick and we don’t know if David knows of Merrick’s fate or not because that is the last we hear of either of them, really.