Welcome to the forum!! I read your entire post and I have some feedback for you.
You said that they had previously talked about introducing a girlfriend for them both to share….then you all discussed about you being in an exclusive relationship with them both.
You agreed to that because you initially enjoyed being with both of them, you were physically attracted to them both and you had a great time with them. But, once you realized that wasn’t working exactly as planned, you began to consider yourself as a secondary. Now you realize that your needs aren’t being met in this situation. Not only that, but you are now trying to rescue her and have developed what seems like a codependent relationship with her.
This is what I would suggest. Attend a few Al-Anon meetings which will help you get “detached” from her dysfunction.
The next important suggestion I have is that you begin to give yourself permission to find a partner or partners that can meet more of your needs.
The good thing about Polyamory is that there is no certain set formula for relationship configurations. If you spend some time reading this forum, you will see all types of configurations. There is no reason why you couldn’t take on another lover or two while still seeing him and/or her if you choose.
This is my opinion…….Your triad relationship is under too much pressure because of the idea that it is closed and the three of you went into it hoping you would all get your needs met within the triad. Now that it’s obvious that you will not, it’s time to expand your horizons…..just my opinion!!!
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.