For me, I never tried juggling multiple women like that. After seeing my friends try, it always ends in disaster. That's my lesson.
The main thing that ruins the 'side chick' dynamic is "Time".
... the more encounters, the more chances to get caught, the more chances a pregnancy can occur, the more wrinkles show up around the eyes and choices have to be made to lock down the person you're with even if it means muscling out the other girl..... eventually fate will force you to choose one girl or the other, and unless you're some free-loving hippie with too much bitcoin wealth to find two women to agree to a polyamorous relationship.... eventually the side-chick will leave or complicate your life into alimony bankruptcy....
That's why I just go with providers... simple clean, quick, brief business transactions that can sever the connection when needed; being respectful of course, but at least the intentions are known every time there is an engagement.