IPA: /ˌhɛtəroʊˈsɛkʃuəli/
KK: /hɛtəroʊsɛkʃuəli/
In a way that relates to or involves sexual attraction between people of the opposite sex.
They expressed their feelings heterosexually, showing their attraction to each other.
Heterosexually → It is formed from "hetero-" (from Greek "heteros", meaning different) and "sexus" (from Latin, meaning sex or gender) and the suffix "-ally" (meaning in a manner). The word describes a manner of relating to or being attracted to individuals of the opposite sex.
Think of 'different' ('hetero-') relating to 'sex' ('sexus') — this helps you remember that 'heterosexually' refers to attraction to the opposite sex.
No commonly confused words.