Ooooooo, fascinating visual idea! Simple, yet compelling! Hope you do something more with the idea!
As to what drew (or pulled) them apart from each other, how's this for an idea: Suppose it would be a sort of violation of the social customs on their world (or galaxy or whatever) for robots & green-skinned aliens (whatever their species is called) to be close together on too-personal social terms...? Not so much against their laws per se, more of a social disapproval: "Oh, my dear, we don't socialize with **their** kind!" And anyone who violates that custom is sort of ostracized from others of their kind. Or something.
I dunno...just a thought... (I've been watching a lot of "Downton Abbey" lately & the idea just popped into my mind...)
Anyway, it's a really beautiful picture & I like it a lot!