The only time he does not talk to me is when he is with his other girl. His focus is on her, I imagine. So I fear I will lose more of his time when he gets yet another girl. Or if he meets another....and another. I do know a few people in six committed relationships at once and cannot even fathom it. I fear I'll eventually fall to the wayside since I view myself as least interesting of the girls he has been with that I know.
This isn't necessarily insecurity. The time factor is a very real part of polyamory and one of the many reasons why people choose not to have non monogamous relationships. I know you said something in your thread about never letting a new relationship affect your old one, but in reality, resources like time are finite and every new relationship you start will take some time and attention away from your other partner(s).