As they say the definition of madness is to do the same thing over and over and expect a different result. She is just not that into you. You haven't the NRE, she wants the husband more and you can't really be sure if she want to be with you or only appeasing you to have more time with your husband. Eventually you will be more estranged from this triad and by vetoing your plans to open the relationship so as to get your own girlfriend, your husband is controlling you, guaranteeing that 'he' is the only one enjoying this Poly lifestyle.
You need to start putting your foot down because this is not a triad, it is a vee with some appeasement to your need for female attention. Woman up lady and get your own girlfriend and don't let husband anywhere near her!