Bisexual refers to being attracted to people of both the same gender as you and different gender as you, so it already covers things outside the binary.
It’s a common mistake though, many people think the bi part means attracted to both men and women (excluding anything else).
Edit for clarity: the bi part of bisexual refers to both homosexual (same gender) and heterosexual (different gender) so nobody’s left out. I guess an argument could be made that an agender person might not fit under either umbrella, but i would still consider agender to be either same gender (if the bisexual person is also agender) or different gender (if the bisexual person is not agender).
Bisexual refers to being attracted to people of both the same gender as you and different gender as you, so it already covers things outside the binary. It’s a common mistake though, many people think the bi part means attracted to both men and women (excluding anything else).
Edit for clarity: the bi part of bisexual refers to both homosexual (same gender) and heterosexual (different gender) so nobody’s left out. I guess an argument could be made that an agender person might not fit under either umbrella, but i would still consider agender to be either same gender (if the bisexual person is also agender) or different gender (if the bisexual person is not agender).