How many partners?

I'm guessing you're referring to straight-up Romance here & not Women's Fiction, but I think it could work in either (admittedly, I have very little experience with straight-up Romance, so take this with as many grains of salt as desired).

Depends on the situation: if the hero is in a commited relationship & having sex outside it - that'd be a big NO - but I can see many scenarios where it wouldn't be a stretch. Especially if the h/h have known each other for a while. Him having sex with two women in one week doesn't necessarily scream to me "can't control himself/ruled by hormones."

But, maybe that's just me.
I hope not, though, because I have more than one MC who has sex with more than one man during her story. I don't think it makes them less sympathetic, but only readers will know for sure.

A promiscuous person is-- as I've been given to understand-- not romantic. But I could be wrong. I'm out of my league here, so.. I dunno. (I give it to my homies yo.) I've noticed during my overly-long existence that humans are not monogamous even though they claim to be. Even my doves-- who do mate for life-- have affairs on the side, though their reasons for doing so remain obscure. To me it looks like they are having a good time, but they don't tell me what's going on in their heads, if anything. A male dove will fornicate outside of his relationship, but mourn sincerely when his female has died. They're animals, though, so-- who knows!?

I hope this was helpful, but I'm sure it's probably not.

I have no problems with a hero or heroine sleeping with two or three people over the course of a novel, and threesomes can be hot, but it's important that once a character is in a loving relationship with another they don't go have meaningless sex with another character.

The hero or heroine might start out promiscuous--in fact, one of the factors keeping them apart might be that the man is a playboy, and she isn't sure she can trust his intentions (same can apply to the woman). However, I think that for it to be a romance, there then has to be a character shift by the end (as part of the romantic aspect of the plot)--he starts out as a playboy, having nothing but physical relationships with little emotional committment, but then his growing emotions for her cause him to change his ways (just as an example). I think that having sex with more than one other character can work as long as its worked into the overall change of character.

I dont think that sleeping with two people in one story makes a person promiscuous. What if the person is in one relationship which breaks up and then the MC meets the HEA character? Does that make her/him promiscuous? Obviously, we're not talking about someone sleepign with everyone he/she meets because that would take it out of the romance genre. But within the genre I don't see it as a problem, depending on what you're writing. It all comes back to what you're writing.

My heroine has sex with 4 men over the course of the book. When I first wrote it, she only had sex with two, but then I decided that real single women of her age would have more partners so I gave her a casual encounter, just to relieve the pressure of not having a sexual partner.

I would see sex with anyone other than the destined partner to be highly unusual in romance genre. The exception being in polyamorous romance where this is more than one destined love-match so the sex is still within the primary romance--I can see it also in genres related to swinging or voyeurism where it would not count as infidelity. I think that in genre romance there is an expectation that one the romatic unit meet, sex will be within those bounds unless there is a clear plot-based reason. (Yes, my first romance contains infidelitiy during a relationship 'reversal', it took some convincing to leave that scene in and only when it was presented as a negative experience).

My book is Women's fiction rather than Romance, and the story takes place over the course of many years.

Women's fiction and the course of several years? Your heroine can sleep with anyone she wants and as many as she wants. It's only in category romance, ie Harlequin books, that they don't want anyone but the Hero in her bed. You are safe.

I think if your MC is promiscuous and then is reformed by love, that would work. Or if your MC is a prostitute, but loves a certain someone (Memoirs of a Geisha, Pretty Woman). Or if your two lovers split up, mess around for a while, and then get back together and forgive each other, or if MC falls for two people and has to choose. These are all good options to me.

I just read Wild Seed by Octavia Butler and in it both her MC's had multiple partners--though not always by choice.

Also, being of a SF/Fanstasy bent, I think if the culture of your MC is accepting of promiscuity--for example, mating is viewed as something for procreation, which is regulated by other elements of society (mothers, grandmothers, etc.) but lovemaking would be a personal decision--and procreation would be prohibited under those circumtances... (OK, too SF for this genre?)

People tend to disagree, sometimes violently, over what constitutes "promiscuous" behavior. The dictionary is rather blase on that account, and leaves a great deal open to interpretation. Clerics and evangelical types (and even a great many pagans, atheists, etc.) often tell us that sexual behavior with more than one person in one's life is a foot on the highway to hell. One can sense, if one is anything approaching a normal human with the usual urges, that these definitions leave something to be desired.

In the context of romantic writing, it's pretty usual for the female heroine to be "lusty", full of appetite, and capable of multiple orgasms. That's why I avoid reading romantic fiction (well, if there's a romance novel in the bathroom at Mom's house I might have a peek), because: How is a female human supposed to become that "lusty" when she's totally inexperienced? It doesn't seem realistic in the least.

I mean, love can only go so far and no further when it comes to filling in that gap between urge and mechanism.

I realize that romantic fiction is geared toward an audience that is devoted or committed, in one way or another, to the ideal (if not the actual practice) of having only one sex partner for life. I suppose that is a worthy ideal in a sense, but-- wait, no, it isn't worthy in ANY sense. Forget that I said that.

Anyway: Whether it's worthy or not, the descriptions of romantic and mechanical sexual behavior between hero and heroine are in the ideal sense supposed to supply some of the heat that is lost in a long-term monogamous relationship WITHOUT making the reader want to drop what she is doing to run and put an ad on Yahoo Personals-- "looking for that special strong-armed stableboy". It's a razor's edge, in other words.

THERE'S the worth and challenge of romantic fiction! And frankly, it's a challenge I admit I'm not in the least equal to.

I would agree with the above posters that if a romantic heroine has sex with more than one partner in a novel, it should either be by some type of unhappy circumstance or error, and/or depicted as a process by which she learns that romance should lead her life decisions.

See, I can say those words, but I can't translate them to anything intelligible as far as a story. Oh well... no one's perfect... Frankly, the sluttier and more unprincipled someone is, the more I tend to like him or her. My life history will NEVER become the subject of any type of romantic writing, at least in this continuum.

I hope this was helpful!

I'd like to see the word "promiscuous" deleted from the language - I think it's an aspersion, not a descriptor, and I have never liked the way it has been used to judge women.

That said, I think the number of times a man or woman has sex in a book is determined by the reality of the story and by the confines of the genre (or publishing house) you are writing for. Harlequin has strict guidelines, as do a couple of others. I think so many romance stories rely on the hero and heroine discovering each other and eschewing others once the depth of that discovery is made. That makes for a very satisfying ever-after.

But I also think real people behave differently, and no matter how serious your MCs are about each other, the delicious outside temptations are bound to give a lot of reader interest, especially if they are described well.

Maybe there's no set number - and every book is different...