WTF is with the all-caps? Not needed, thanks.
This is situational and based on individual relationships and has no right/wrong answer, except for within the context of your own relationship. My current GF has sex with other men, mostly when I'm present! There is no jealously or resentment, it's an integral part of our sex life. Right now I'm having a bit of a fling, for lack of a better word, with a woman involved in the sex industry, and of course my GF is well aware of it, and it was discussed with her before it became physical. Upfront and honest is the best way to go. The deal I have with her is I only see this other woman while my GF is out of town - she travels quite a bit for work. Am I jealous that my fling is spending her days having sex with other men? Nope. But that's me and the women I'm with, and you might not be able to cope with this situation, so don't put yourself in it.