The warning of exacting a "price" assumes a necessary balance within her life, perhaps implying a moralistic or cautionary quality is involved in D's ability to exercise her sexual desire in whatever way is available to her that seems attainable or interesting.
So, there seems to be an undercurrent in your post which implies that D's exponential ramp-up of sexual experiences and initimacy with friends, acquaintances is somehow an aspect of life which must necessarily be curated or that it comes with a balance of expense. It's merely another form of her blossoming expression from within, enabled almost fully by a combination of F's desire to support her happiness and those she meets wanting to get in her (or her partner's) pants. Given that her only other priorities in life are firming the definition of her lifestyle with F at its core - which includes long-lasting income options and a mutually desirable living space - she literally has only her imagination holding her back when it comes to expressing herself in this sexual hobby.
And that's what it is for her at this point: an enjoyable activity, without remorse and filled with verve to experience more, wondering what can come next as much as appreciating what she already enjoys.
Her rampup in sexual activities has not made D drop career plans, desire to own a home and to marry + procreate with F - if anything, she apparently feels closer to him from all the trust and open experiences they have shared, discussed and mutually allowed.
Sexuality can be a valid aspect of someone's lifestyle, there is no need to view it as a limitation to other aspects of her life simply because she has so many options available from which she might sample and dig deeper into exercising.
Anyone seeking to remind D that she has limits on sexual tastes and forays - even while she's still successfully balancing other aspects of her life which are both necessary and fulfilling - would seem to be placing their own values upon her. In the reality of Donutistan, I have a feeling D would find little to learn from if such abstract ideals were offered to her as a warning or guide for her life when all evidence suggests she's doing just fine.