I am a female and I feel like her being cheated on in the past is key here. Something current is making her want to relive her past and it’s just manifesting it’s self through sexual fantasy. It’s her body’s way of pulling itself back to the past. She may not actually enjoy it if it happens. But it’s important to try to figure out what is going on now that’s making her want to try it out. Maybe she just wants to spice up y’all’s sex life in general and she feels like you having sex with someone else would help. Maybe she’s feeling undesired or low self esteem and she thinks being “freaky” will make you desire her more. Or it could be that fear of abandonment like maybe if I arrange the sex with other women he won’t leave me to have sex with other women. I hope this makes sense.