I heard it said once that you can't expect one person to fulfill all your needs. Humans are very complex beings. We need social interactions, emotional support, intellectual stimulation, physical touch, etc, all to varying degrees. It is unrealistic to put the responsibility on one other person to fulfill all those needs. That is why in addition to our life partner, we have other relationships. One friend enjoys the same books, a family member understands your quirky humor, a neighbor shares your passion for gardening. All of these relationships are necessary to our well-being.
The struggle with being bisexual (in my experience) is that our physical needs by nature can rarely be met by one person. I love my husband. He grounds me. He makes me laugh. He builds me up, and supports me when I am weak. He listens, and shares his heart. And I am so grateful for him every single day, but he is not enough. I know who he is and I enjoy that person. But I do not expect him to be everything for me because that is an unrealistic expectation. He knows this and understands this (in his own way). Hopefully my relationships keep me sane enough to make it through till tomorrow.