Someone who is repulsed & feels threatened by by intimacy between non same sex peoples.
An asexual person has heterophobia & semihomophobia; being perfectly fine with gays of the opposite gender who pose no personal threat of amorous ambitions, but disgusted by straight persons of the opposite gender & gay persons of the same gender.
The aversion to persons of the opposite gender stem from a misandric or misogynistic upbringing. The distaste for sexual persons of the same gender are resentment from an inability to sympathise with a person who would intimately fraternize with the person of the opposite gender. The disgust in the gay persons of the same gender come from the threat of being flirted with & because straight members of the opposite gender seem to have a fetish for gay members of the opposite sex.
(Yes, straight women DO fantasize about gay men, It's called yaoi).