Riley Vashtee

Riley Vashtee was a crew member of the S.S. Pentallian, a ship mining from the sentient star Torajii. Shortly after Martha Jones arrived onboard with the Doctor in his TARDIS he developed a strong attraction to her. While trapped in an escape pod and thinking they would both soon die in the fires of the star, Martha reciprocated Riley's sentiments in what they thought was their last minutes together.

The Doctor having rescued them, though, Martha kissed him on the lips before she departed in the TARDIS with the Doctor, leaving Riley to his life on the S.S. Pentallian. (DW: 42)

Dialogue in the episode, combined with references on the Doctor Who website, implies the character is bisexual.