There's also the idea of using sex in theurgic work with the aim of performing a
unio mystica, physically and in a ritual context, for example in Tantra where the male becomes Shiva and the female Shakti. Since it's a closed and very secretive practice, accounts vary how and to what extent of intensity it's still being performed in India today but in any event, it should be seen as part of a radical yogic tradition that encompasses very much more than simple antinomism but of course people will inevitably latch onto that aspect of Tantra, just as the Karma Sutra isn't just about sex but is nevertheless seen exclusively as an erotic manual.
The practical difficulty is that both celebrants will start out as humans before becoming gods and godesses, with all their flaws, quirks, and preferences concerning potential sexual partners. When I was younger, I spent some time in the NeoTantra scene, went to numerous weekend workshops and even participated in a six-week program held over the course of a year. I can now see the similarities of NeoTantra and genuine Indian Tantra - the idea in both systems is to purify oneself to prepare for
and for becoming one with the devine but while in India this is achieved by years of Kriya Yoga, Western NeoTantra takes a psychotherapeutical route with all sorts of ingenious exercises to get rid of any mommy-daddy issues, vestiges of religious hangups, bodyshame and whatnot first. 'Sacred sexuality' or not, the group setting will help you develop a more pragmatic attitude towards your body - I'm naked but so is everybody else, so what's the big deal? We got so used to it that we even came up with a jocular expression: "Dress code for today? The usual outfit!", i.e. none.
The workshops I went to were quite gentle, NewAgey, and vanilla but I can well imagine that such Tantra-style sex magic can become problematical in a magical order context. When it came to choosing partners for exercises, for example, the same man and the same woman always got left - he was weird, she was irascible and unlikable, both very unattractive; if I had had to practice divine sexual union with either of them, I'd probably run for the hills but then I had the choice and wasn't under any sort of duress or group pressure. Strictly religiously (or ideologically) speaking, their personalities or attractiveness shouldn't have made a difference since the divine resided in both of them, too, but in practice, it mattered a lot.
For this reason, theurgic sex magic may be probably best practiced within the confines of a relationship instead of a group setting. There might still be some real issues with your partner but at least you're dealing with a familiar person and will have time to work them out in everyday life.