Do you guys who are spinning plates care if they are with somone other than you?
From my experience, when you're messing around with multiple Women, there is a very high probability those Women are also talking to and messing around with other Men.
The only way she wouldn't be is if you are acting like you want a relationship with her and actually want to be with her but even then, If you and the Woman have not discussed being together, she's more than likely messing with other guys. at the bare minimum, talking to other guys.
Another point is how much she values you compared to the other guy(s). She will be more lenient towards the guy she REALLY likes compared to anyone else. This is why a girl could be messing around with you but when the guy she really likes wants more of her attention or wants to be with her, she vanishes and ends up exclusively with that guy even though she's been fvcking around with multiple dudes.
Many Men are under the illusion that they are the only Man that Woman is fvcking, ESPECIALLY if that Woman is a 7+. This is why it's important to be upfront and straight forward with what you want from Women. They are masters at making you "think" you are the only guy but a Man with experience know's she's full of sh*t.
Hey, Women are very horny too, I would argue more so than Men, so they are looking for multiple D*ck if they know they aren't with someone exclusively.