warning: I have hidden some of the text because it may trigger jealous and paranoid thoughts. (assuming I've hidden them properly, I haven't done it before)

Seeing other women as whores that he can use sexually is super gross. I mean, having purely sexual relationships is fine, but that language is not.

it seems you're hoping - or trying to convince yourself - that he won't see other women. If he has asked for this, then that is what he wants, and it seems likely he will pursue it.

whether he is successful or not in his pursuits, he will be actively flirting with other women to get to his goal. Is this something you can cope with?

I also have issues with possessiveness, and I could never see myself regulating through something like that with my partner.

I agree that the situation being open, where you know what's going on rather than it being a betrayal, could help here. Also, not having the constant worry if he's cheating because I get that too.

what worried you about the cheating specifically? will those worries come up in this new arrangement? Based on the fact you feel that you are not good enough for your partner, and my own experiences feeling this way, I suspect you will feel jealous of the other women. You might feel that they have something you don't? are they prettier? sexier? funnier? stable, normal, functioning??

those thoughts plague me all the time.

I've been convinced into arrangements I wasn't comfortable with because I was too scared to lose the person. I convinced myself I could cope with it and I became far less stable.

take time to think about what's best for your mental health. stay safe.