For the better, of course

Being with a Paya is amazing because they are so adaptive to your desires and helping bring you to new heights of mutual pleasure. Both men and women get a lot out of it. So "monogamous" now means "having one partner and any number of Paya." A lot more people are polygamous, too (like the Paya themselves).

Kids are taught in sex ed that while you can use a Paya any way you want, you should take some time to learn from them to make you a better lover. Most people lose virginity to them, with the experience welcoming and forgiving.

Most marriages are between humans; Paya's sexual habits mean they can't give most humans what they want in long-term commitment and presence, even if they want to in theory. But if you're getting serious with a boyfriend or girlfriend, a relationship milestone before moving in together is to find a Paya threesome partner to help you sexually mesh. And many human couples and polycules will find a Paya friend to move in with them as a long-term roommate/sex partner. (About half the Paya do form long-term partnerships with other Paya, especially the few that have litters.)

Here's an example of how you can use Paya for pure pleasure or for personal improvement. In the "VC mod," a female-form Paya can alter her vaginal walls so that skin has the same erogenous response as a penis head. That lets them have sex like porn and hentai used to portray it: pure penetration, with zero clitoral stimulation, genuinely drives them wild. It's not frowned on for people to use this mod - it's fun! But at least some of the time, men are encouraged to fuck a Paya with the human-standard vulva, so they can know how to treat human women.

About 70% of humans are bi-/pan-sexual, 10% gay, 20% straight. Given all the fun ways Paya can alter their genitals, "straight" doesn't mean limiting yourself to one set of equipment. Of course these distinctions mean nothing to Paya themselves.