It seems like being secondary isn't ok with you. I don't blame you; it wouldn't be for me either. I'm in a vee with a married couple (husband is the hinge - his wife and I quickly became dear friends). I'm not secondary, and his wife has referred to me as Co-primary from the beginning as she said it was the only way (in her opinion) to make this work.
I would ask for your relationship to be considered as equal to his other. I would ask for communication that shows his feelings for you if that's what you need. If he can't or won't give it then you have a hard decision to make.