<p>Multigender attracted (Bi+) people potentially face different experiences and challenges depending on the gender of their relationship partner/s. While those in same-gender relationships may be subject to anti-LGBTQA+ discrimination or abuse, those in opposite-gender relationships may experience greater distress associated with the invisibility or erasure of their sexual identities. These experiences may in turn impact the mental health of Bi+ people who frequently report worse mental health outcomes than their gay or lesbian peers. Data from 1261 bisexual and pansexual cisgender adults in Australia were used to explore their mental health and well-being outcomes as a function of their current relationship configuration (opposite gender partner, same gender partner, or single). Relationship configuration was found to be associated with mental health and well-being outcomes. This was especially the case for Bi+ women, who reported worse mental health outcomes if they were single or in an opposite-gender relationship. While the effect was less pronounced for Bi+ men, those who were in a same-gender relationship were less likely to have a history of smoking. The findings highlight the need for supporting the mental health and well-being of Bi+ cisgender people, which may include promoting awareness and inclusion of Bi+ identities within both the broader and LGBTQA+ communities. The findings may also have implications for developing targeted interventions aimed at reducing substance use among Bi+ individuals, particularly when single.</p>