NMKNMP= Not my kid, not my problem

I've adopted this "attitude" and S/O and I aren't even living together yet. All of my family and friends feel that if he and I were to get married, that I should take on the mom role. S/O thinks so too. I know most, if not all of you know what I'm talking about. What they don't seem to realize is that I don't want to to take on this role. Maybe I'd be more inclined if I didn't already know that S/O is more likely to dismiss my input when it comes to his daughter than he is to consider it.

Perfect example,

We're going to the birthday party of my friend's twin girls on Saturday so, he's taking her to get her hair done today. She is a bi-racial child and she has "ethnic"(I hate that term) texture hair. He calls me and asks me for advice and I give it to him. He texts me later to tell me he made an appointment and she's getting waterfall curls. I didn't know what they looked like so I googled it. All of the images are of children with hair of a different texture than his daughter's. I know that the stylist will have to straighten her hair in order to accomplish this. This is an issue because he lives by the ocean. Which, anyone who ever straightens their hair knows how much humidity will ruin it. The second issue is that even though this is supposed to be his weekend having FSD he's taking her to her mother's house right after the hair salon and then we're picking her up the day of the party and then taking her back after the party. Which is why he can't take her to the salon the day of the party like he should. BM doesn't comb or brush FSD's hair now as it is so I know she isn't going to wrap FSD's hair before bed so that it isn't ruined. I tell him waterfall curls will not last two days and that he should get some type of braids that won't be destroyed by BM when she's over there.

But he doesn't like braids and I'm like TOO BAD you're raising a bi-racial child. She doesn't have hair like your mom or your sisters and she won't ever have hair like that. The only way to accomplish getting that type of hair for her is to get a wig or a weave which she doesn't need because she had a FULL head of gorgeous hair of her own. Although he's thrown out all of my suggestions so far he keeps asking, "well what can I get besides waterfall curls?" and I'm like I f***ing told you already dude. He's going to do what he wants and I'm throwing my hands up and saying, f**k it, she's not my kid and it's not my money. If she were my child I'd take her myself but she isn't. My family and friends are always saying that I can't treat her different than the children I don't even have yet but I'm like WTF do you suggest I do in this situation huh? I can't kidnap her and then get her hair done in a style her parent hates. I wouldn't even be against waterfall curls if we were taking her the day of the party because that would make sense but we're not. He's taking her today and then to her mom's. Anyone who curls their hair with curling irons knows that s**t isn't going to last very long the day of, let alone the next day and after it being slept on.

That's my rant for the week.

Have a good weekend everyone.

:::Edit::: Also, I have the same texture hair so I really do know wtf I'm talking about but he still ignores me