I'm not sure how that works?
You're either able to pursue all love interests and maintain relationships with them or you have to choose one interest over another due to constraints in time/plot.
Help me understand how both would work.
Both means they like the option of both available, so they can choose 1 or all.
At their core, if you want a decent story AND a harem, then you need to do it right. Using Incest as an example, Incest itself is littered with consequences should you stop partway. Once you get deep enough into an incestuous relationship, it's increasingly doubtful you could ever return to normal, a card authors play when starting things out. Once you've gotten far enough, stopping runs the risk of ruining your relationship with said relative, and creating drama amongst the family.
Now, take that, and extend it to multiple relatives. They find out about each other, and suppose they forgive your cheating, the question then becomes. Are they willing to "Fight" or "Compete" with a beloved relative in order to win you for themself. Whoever backs out of the arrangement for any reason, is running the risk of being estranged from those they care about the most, as well as losing you who should be the one they love. They may not want to hurt family, which they will if they keep you, but that means giving you up, and even if they give you up they may still lose that close bond.
This gives credence to a degree, over why incestuous harems have a better leg to stand on, as it frees up the ability to actually be "Open" about your relationship, and if they find incest itself hot, they can now explore their more bisexual side with their other relatives.
Stretching Incest to include Non relatives. Usually these girls only appear in harems under one of two circumstances. 1) They are very close / in love with a relative in question or 2) They are incredibly kinky and find incest hot, often a bisexual girl whose also interested in having sex with the family.
Why? Because any girl that doesn't fit those criteria has the big barrier of "INCEST IS WRONG" to cross over to even consider a polyamorous relationship, let alone cheating and whether she even stays with you for being an incest creep.
I honestly feel that a true harem should involve more open communication amongst the related parties. It's one thing to "Fool Around" with multiple people, another to be "In a relationship" even if it's not outright stated. I'd prefer games that involve characters being more aware that the MC is involved in other people, whether they know of them or not, and a point is made when things are to take the next step. Games that involve a Side-Kick heroine that encourages harems and actively seeks to assist are quite helpful.
Another aspect that could help is simply the Harem Owner being more virile than their partners. Imagine a girl that has a libido on the lower side, partnered up with someone on the higher side. These sort of relationships can often result in the Higher partner being allowed to have sex on the side by virtue of the fact they currently have needs that aren't being met, and both feel it'd be good for the relationship if someone is meeting them. This limits the notion of being unable to satisfy that many women all at once. Taking Echoes of Lust as an example, one of the more problematic aspects from a literary standpoint, is one of the characters flaws (IE, something that delays sex) is that he is a quick shot, whose never actually engaged in sexual acts back to back (Though he claims he could). A guy like this, reasonably, shouldn't be able to please so many woman who are constantly dissatisfied with him finishing, especially if they have to share it. Now, if his endurance / libido goes up, this doesn't become as big of an issue, but is currently one.
My last comment is that, I've said this months ago, but the current style of games with multiple girls usually follow one of two options 1) Their content is interconnected and you can't do one without the other or 2) You can run their content simultaneously until you ultimately have to make some kind of choice.
Personally? I'd prefer a game that had overlapping schedules from girls, where actively courting one becomes detrimental to another, either making them suspicious or less interested. This offers more replay ability and consequences to your decisions. In games of this nature, I'm more partial to actively NOT choosing to be with certain girls, as I want to focus exclusively on one in particular, and will come to them on another playthrough.
As far as Multiple guys go, I simply say that for me to really go through a "Sharing" route, or happily go down something remotely NTR long term (IE, doing it for a full playthrough rather than one scene), I'd have to genuinely like a guy. Take the Best Friend from Acting Lessons. That sorta guy I'd have no issues having a "Sharing" path. Such a path also opens up to more Homo-erotic paths (GuyxGuy) if there is enough interest from those that would enjoy it.
TLDR
Lots of ideas, Lots of work involved, ultimately up to you. Your best bet is to give options so people can do what they prefer, and I'd definitely consider getting someone good (Or even beta readers) to check through Harem resolution or overall story to make it as less "Heres a girl, and heres another!" that most games currently sit within.
So to better understand, is it a problem with the female characters having relations with other men or is it a problem of the MC cheating on the single love interest?
