Heteroflexible

Heteroflexible or Elasexual is used to describe an individual who is generally straight/heterosexual and primarily experiences attraction to the "opposite" gender/dissimilar genders. But, they very rarely have tendencies to be attracted to the same gender. People who identify as heteroflexible may identify with this label only, or they may identify as straight. Heteroflexible people can be considered bisexual or otherwise multisexual, however for some their attraction to the same gender is so rare that one may not consider bisexual to be an accurate description of their orientation in most situations.

Kinsey Scale
The Kinsey Scale is a way to determine one's sexual preferences through a test. Once one takes the test, they will be given a score from 0-6; 0 being exclusively heterosexual, 6 being exclusively homosexual. Heteroflexible individuals will usually fall at about a 1 on this scale.

Resources

 * 1) https://www.deviantart.com/pride-flags/art/Heteroflexible-1-543925646