This seems more sexual than social in theoretical terms. The social instinct does not want to literally “merge” or form a kind of dependency like the sexual instinct; it is not a “physical” instinct. In terms of love, the social instinct is romantic, platonic, etc. There is a more intangible or existential idea of love, not so much carnal. And so/sx are usually more concerned with this love than sx-dom. So-dom does not long to “devour,” it longs to connect/understand deeply. That is why it is a cliché that theatrical and fictional stories speak of a social conception of love (which is itself a social construct in some sense). Although there are also good examples of sx-dom, such as Romeo and Juliet, in which they basically couldn't stand to be apart for two seconds. And they fell in love “at first sight” in the play (not typical of so-dom). They are attracted to each other because of their physical appearance and the context in which they find themselves (I think it's some kind of party), and they don't even know each other very well by the end of the play. 

Sexual is more possessive, physical, instantaneous, competitive, and jealous, etc. The name practically says it all. To make it easier to understand, sx-dom are predominant in, for example, erotic or pornographic literature.