Living with a mistress as a default solution to a late single life

It is difficult to permit married life without Kiddushin, because quite simply it is against Halacha. It is true that some have written that it is permissible to have sex with other people (like the Ya’abetz), but the issue is quite vague. Zvi Zohar dealt with it in his controversial (and very problematic) article in Akademot, and see Rabbi Shmuel Ariel’s response on the matter (I don’t think it was published in Akademot, but it can certainly be found online). I assume you can find materials and reviews online. But there is a general consideration here that I do not understand regarding the background to your question. If it is a permanent relationship – then why don’t you marry as a demigod, and not live in a mechanism of mistresses, which is certainly not the proper halakhic path? And if it is a casual relationship – then there are no mistresses here, and that is certainly forbidden. In short, I don’t see a possibility of allowing such a thing, unless there is a special situation that I haven’t thought of. “It would be better if there were more gullible people” doesn’t belong at all in a question like this, since I assume you don’t expect me to mislead you so that you will sin unintentionally. If you’re asking, you want to know and not be unintentionally.