Hey, SrAh... thanks for pointing out what the other shoe is like! That's a bit helpful. And I do feel like that on occasion (convincing myself of crazy things):... He'll be with the newbie soon enough instead of me. Why are we moving in together, when he clearly wants to be with them instead, etc., etc.
I don't know that it would benefit the situation pointing out how he would be hurt about things... in the Meyers Brigg personality type, he's an INTJ (basically Spock or Sheldon from 'Big Bang Theory'). Not much phases him.
It would probably serve me better to tell him what behavior I want (as GalaGirl recommended): Please pour your energies into us when we're together. An occasional text (not a full conversation) is okay.
Thanks for replying and being helpful!