No absolutely not. It has to be a triangle. I am bisexual. And We come Looking for what We are looking very bluntly. A bisexual woman willing to be in a triangle relationship. We both have discussed what We are looking for And what We want. Anyone who gets involved with us must know We will never do anything on our own. Our point in this is to enjoy each other all three of us. Together.
From a long history of being involved in polyamory and having polyamorous friends, I'll say that what you are seeking is incredibly rare. Obtaining a woman who is sexually interested in both of you for one night can often be challenge, let alone over the long-term. Even when you do meet someone who is interested in you both, that interest often varies: again, from my experience and that of others I have spoken with, it is often like a "friend-with-benefits" with one spouse and a fully involved romantic partner with the other. This can lead to problems between the married couple because one partner feels left out. Particularly, I have to say, when it is the husband and girlfriend, or the wife and the boyfriend who have the "full" bond.
Then, on top of that, many bisexual women don't want to restrict their sex lives purely to threesomes. I may have misinterpreted what you meant by "We will never do anything alone", but one on one sex is something that many, if not most people need in their lives. I am bisexual and there is no way I would give up one on one sex, but I have been in triads, even closed triads. But because I was allowed to interact with my partners as individuals, it worked for me, and many bisexual, poly people I speak to feel the same. Of course, this may be less of a problem if you are okay with the prospective new match to seek partners outside of the triad you seek.
Would you be willing to also sacrifice sex with your husband one on one? Or would this be an expectation that only the new person would have to meet?
It often helps to ask yourself as a bisexual, poly(?) person whether you would accept what you are offering the potential new match. I suggest you list down the expectations, criteria and rules that this person will have to adhere to, and ask yourself honestly if you could create a healthy, fulfilling relationship with another couple under those conditions.