First of all, she wouldn't have had sex with you if she didn't want to have sex with you.

Second, why are you making this more than it is? You've already established that you aren't having a relationship. You both got what you wanted.

Third, you can still be friends and fuck each other. That's what FWB literally means. Just don't catch oneitis and you're good to go

Quit hamstering about what it all means. Let her hamster it up and don't be a bitch about it.

Act like nothing happened, do whatever you were doing before, the woman is the one that pushes for more in a healthy relationship. At that point it is your decision as to whether or not you accept it.

I'm going to go ahead and guess that you made some SMV improvements over the course of your friendship that lead to this point as she now sees you as a sexual option. The worst thing you can do is start acting needy and different to what you were before as it communicates that you get no pussy which is unattractive.

There is no need to be aloof, if you value her friendship then try and do a 180 and friendzone her. If you just want to fuck then your probably going to fuck up the friendship, in that case only hit her up when u want her to come over for sex. Otherwise don't bother interacting with her much.

Yes be aloof and let her do most of the chasing, like 80% of it. Make sure she's the one hitting you up most of the time. Be very patient and wait weeks if you have to. If she doesn't hit you up, move on or else the beta emotions you speak of might surface. Also, you can still bond emotionally with her and keep her as a plate, and this can be every bit as fulfilling as an LTR.

EDIT

Just an afterthought. You say you believe that she's a honest, good human being. I say chances are this is not true. Throw in a little bit of commitment and you will probably see a change. Commitment doesn't have to mean LTR. Just establish a pattern of calling her 2-3 times a week and see what happens when you have a long work day and don't feel like talking. If she doesn't turn into a passive aggressive beech then you might be on your way to building a unicorn

Treat this as a good thing that happened and continue being friends with her like before. You don't need to put on the "aloof persona". Just chill out. If it turn into something more, then it sounds like you would like that based on your post. Don't run from it.

Been friends with her for 4 years, and have been treating her as the girl I take on dates but don't fuck with.

??? Does it get more beta

“Been friends with her for 4 years, and have been treating her as the girl I take on dates but don't fuck with.“

What is wrong with you?

and only text her when I want something, but now that we banged I feel kind of off just putting her on read. In other words, I can still sense that under current of beta emotion, but I know not to use it (or use it sparingly).

You don't owe her anything just because you fucked her.

I'm wondering how I make this sustainable

Care less. It works or it doesn't, either is fine. Care less by getting MORE OPTIONS.

but I know her real well and believe she's an honest, good human being that genuinely shares a connection with me.

You don't know her that well. She's been engaged in constant PR all the time you've known her, and you've bought it. She's still female dude.

Should I maintain the aloof persona and just not give a fuck about her for the benefit of the cause?

Be aloof, but you don't need to pretend you don't care. Just don't care in the negative sense: potential negative emotions.

Go with your gut. TRP is good but it ain't perfect. See what your gut tells you; go with that, see how she reacts and then use more TRP or more gut feeling. Also keep in mind how smart she is since that plays a huge role in how much af/bb affects her.

Why are you making this such a big deal, your friend just turned onto a FWB...