This is probably my own personal code, but I also include any dishonesty involved in getting sex. For example, if we find a partner who is not illicit according to the usual definition, but if we know that we are only having sex with them out of convenience, it is a kind of dishonesty and in my book at least consitutes sexual misconduct. For example, if we continue to have sex with them when we are planning secretly to get out of the relationship. Or if we have so called NSA sex with someone we suspect may be a sex addict. Again, not listed amoung the illicit partners, but we can have our own understanding of what is harmful to ourselves and others. Bhikkhu Bodhi talks in an interesting way about the precepts, not only avoiding breaking them outright, but also ...and I forget the word he used....staining, tarnishing them by behaviour that does not constitute a black and white breaking of them, but which we know by our increasingly sensitivity re morality to be wrong.
Kammalakkhano , bhikkhave, bālo, kammalakkhano pandito, apadānasobhanī paññāti
(The fool is characterized by his/her actions/the wise one is characterized by his/her actions/Wisdom shines forth in behaviour.)
(AN 3.2 Lakkhana Sutta)