Question: Is everyone in the world like this? (Primarily the sexual attitudes.)
Monoculture is unrealistic, as I'm sure we've all heard. Various global cultures and subcultures will have, and have had in the past, different attitudes towards matters. Consider the difference between San Francisco and Afghanistan, or look at the love poetry of classical Greece (I haven't heard anything about straight relationships in Macedon). You'll have repressive societies where nobody talks about sex, open societies where they do, subcultures where different sexualities are accepted while other people even in the same city hate their guts. You'll have societies where people form huge webs of relationships, societies where they form units of a certain size of mixed genders, societies where one person of one gender or orientation owns a harem, societies where couples are the norm. You'll have societies where one gender is dominant, where one sexuality is dominant, where one gender or sexuality is repressed, or when an even more select combination is in charge (on a social or political level). You'll have regions where genders and sexualities are 'caste' things, dictating your general life path, and you'll have regions where your parents tell you what to do, as well as regions where they specifically don't.
This could get very complicated - that is to say, interesting.
A further complication is considering whether this diversity extends to the humanoid population in the same measure. If races are alignment incarnations, as you've indicated, their attitudes are likely to be in tune with said alignment; if (say) gnolls are the chaotic evil race, they'll tend to avoid large social structures, but enjoy establishing dominance over others. Orientation doesn't matter to the race, but it may matter to the culture... so you might have the following (nasty) cultures:
Matriarchy, where the strongest females rule packs of a dozen or so mixed genders; straight 'relationships' are only permitted between the leader female and her sub-males (who have to do her bidding); all other relationships are frowned upon. A subculture of same-sex relationships flourishes, but is largely frowned upon. Women are the warriors, men are labourers.
Matriarchy, where females rule but anyone can breed when they want (and consent isn't necessary). Women are allowed to have same-sex relationships. Men aren't, but if they are discovered to do so, they are considered to be holy and ritually castrated in preparation for the priesthood. A subculture of people who want consent exists, but is frowned upon. Men are the warriors, but are commanded by women.
Patriarchy, where powerful males of a certain rank can lay claim to any number of women (through some appeal to parents or a ritual hunt). Most women belong to these males, leaving most males alone. Males are allowed same-sex relationships, which are considered to be true love (even ranked males have their favourites). The harem women spend most of their time working on household tasks (crops, weaving, etc); they are permitted to have same-sex relationships, and those that are pure-straight are rejected from harem society and compensate by learning politics or magic, becoming 'powers behind the throne'. Males are warriors.
Semi-egalitarian, where either gender is allowed to rule and take any role. The restriction is that only the bisexual can rule or be warriors; relationships are non-permanent, and sex isn't consensual for the pure straight or pure gay. Some straight and gay people form a subculture that teaches druidic rites; they are frowned upon.
OK, take those four cultural archetypes, and throw up a few countries or regions for each of them. Say there's a country ruled by the strict matriarchy, beside a wilderness region of similar culture; the country (call it Gnora) is ruled by a feudal system, and trophy males are trades as political pawns. The nomads (Esgnans) beside them, however, have no leader, no particular politics, and let their males have more free reign, as their life is harsh and they need every hand they can get. Then, throw in the liberal matriarchy as a nomadic neighbour (Gnukkh) to both; the eunuch priests live in monastaries or roam with their tribes.
The Gnukkh are in cultural conflict with the Esgnans and Gnora over their treatment of males - they use them as warriors, and Gnora women legionairres are uneasy attacking Gnukkh raiders for obvious reasons. In addition, the Gnukkh women can engage in relationships, and the Esgnans have never heard of such a thing - even the Gnora think of it as perversion. They also think it's pretty weird to castrate your males and give them religious authority. Of course, the Gnukkh think the Gnora and Esgnans are needlessly repressive and out of touch with the gods.
The Esgnan nomads dislike the idea of being ruled by a single queen, of course, and think the occasional same-sex relationship in Gnora is abhorrent. So they fight for independance against the Gnora legions too.
That's my big, long thoughts on the matter. I didn't mean to invent a sociopolitical region when I started, you know how these things get away from you.
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