Sexual incompatibility is rarely a good reason to open a relationship. In my experience, a relationship is sexually unfulfilling for one of two reasons -
OK. Thanks for being open to discussion.
I super agree with what you're saying about a hypothetical demanding high-maintenance person having a harem of several people with low self esteem, depression, who are overweight or otherwise physically unhealthy, and how the "demanding" partner can rather easily keep their harem or stable of partners in line and not daring to get other partners of their own.
However, I have a bit of a different opinion about mismatched libidos not being a good reason to open a relationship.
IF a relationship is otherwise excellent, but the libidos differ, I think this could be a good reason to open, whether for full-on polyamory, if desired, or just for a physical relationship, FWBs at most.
1) The people have different sexual needs (this could be likes/dislikes/kinks/libido)
Yes, some people realize when they've been in a relationship for a while, after NRE has passed, they are actually asexual, or greysexual, at best. They might love their partner very much, but just not be interested in sex. This could be an innate trait of theirs, or could happen with menopause, andropause, or medications.
2) (At least) One person doesn't want to have sex with the other.
If number 1 is so much of a problem that you're thinking of shifting your entire relationship, it probably means you're just generally incompatible. Opening the relationship won't solve that.
I respectfully disagree. Sex IS just part of a loving relationship. For some, it is extremely important. For others, they can take it or leave it, and they'd really rather leave it. And some find sex repugnant.
Mother Nature is clever. All she cares about is NRE fueling frequent sex, making conception more likely. I think that NRE can fool asexual or greys into having sex for a while, but then losing interest. This is extremely disappointing for their partner with a more average or actually high libido.
In my own personal experience, I have had both high and low libidos, while in serious relationships, for various reasons.
During my marriage, I had low libido when my kids were small. I think this is nature's way. Breastfeeding changes your hormones and sometimes reduces libido. Pure exhaustion from the expending energy on the small ones on very little sleep also has a devastating effect.
I did have relationship issues with my ex husband, and just a lack of experience myself leading to a fear of enough open communication, which also took a toll on our sex life, even before we had kids. However, I loved him and he loved me and neither of us wanted to break up, nor did we cheat. He resented my low interest, but he was patient most of the time. We went to counseling.
Once menopause hit me, my libido skyrocketed, and despite ongoing relationship issues, our sex life increased to where we were having sex every day. This lasted for years, even as we did marriage counseling and ultimately broke up.
Now, with my current nesting partner Pixi, her sex drive was pretty high the first year of our relationship. And she told me how it was even higher when she was younger. But she suffered from chronic anxiety and ended up going through a hunt for the right anti-depressants. One of them reduces sex drive. Other meds she takes also reduce her drive. Most of the time, she'd rather think about sex than actually do it. This is frustrating for me. But we are crazy about each other. Luckily we are polyamorous and I can get sexual satisfaction from others (and love, as well). Pixi's bf's sex drive is on the low side, it seems, too, so there isn't a mismatch.
Number 2 is more complex. You'll see that many of us immediately ask a cis man wanting to open the relationship for more sex if he is helping to sustain a healthy relationship at home by contributing to the household in a range of ways, if he is trying to sustain his appearance and hygiene, if he is skilled in bed.
We don't always ask a cis woman those same questions. We assume that she, the female nurturer and servant (tongue-in-cheek), is a loving, warm, sexually skilled being who would never compromise the mental health of her loved ones until their sex drive diminished by their low mood.
A lot of the time, men who are substandard or even abusive partners won't even know that there is a sexual issue in their relationship. Why? Because their partners often don't need to be aroused for intercourse to occur. Or rather, for penetration to occur.
People with male partners often find that they feel a pressure to please their male partner. I'm keeping this gender neutral because you find this sort of heteronormativity in gay relationships too. Those where hegemonic masculinity is a prevailing trait of the dynamic.
So these cis men often have no idea that the sex they have with their partners isn't mutually desired or enjoyed and is therefore coerced. In the worst case scenarios, it's forced.
I don't have much to say about this except that it is a shameful product of the patriarchy.
Cis men do need an erection to penetrate. That often can't be mustered when someone is suffering from low mood, even with medical aids like Viagra. That's not how it works for them.
Sure they can do other things to their partners, like give oral sex, but many people with male partners are focused on their penile arousal. They'd view it as rejection if their partner was rarely turned on by going down on them, for example. And my experience with cis men tells me that they can be lackluster with their efforts if they aren't aroused when doing these activities. They don't need an erection, but their mind needs to be into it.
And of course, an aroused woman will give better oral than a woman who isn't particularly into it. Unless, that is, she's getting a monetary reward.
Personally, I'd prefer they didn't bother if it is just a dutiful offering. And I think many people with male partners would say the same. That's why when low mood in a cis male is what makes a relationship sexless, it really is sexless. Everyone will know it.
What happens then depends on the people involved. Some weaponise low libido as part of their wider campaign of abuse against the leas desiring partner. That's few though. Few people are that malicious.
Many more will mistake the low mood for a sexual incompatibility and wander into dead bedrooms or an asexuality website. Some come here and use it as a motivation to open their relationship.