Okay, here's my viewpoints:
Madhu is helping Sultan only because of Aryan. She isn't falling for him. She doesn't love him. She's not moving on from RK to Sultan. All she's doing, is helping Aryan because she thinks its the right thing to do. And that there was the foundation of Madhu's character: doing the right thing. And in her mind right now, the right thing would be to make sure Aryan, an innocent kid, is okay. If you recall, she doesn't like Sultan at all. She wanted to separate Aryan and Sultan. But she's tolerating Sultan because she's seen how much Aryan needs Sultan. That day when Aryan stayed with her when Sultan was gone, that's when she realized that despite how much she dislikes Sultan and whatnot, Aryan loves and needs him. And the whole backstory of how Aryan's mother left him, she's beginning to see that even with his harsh methods, Sultan loves his son and Aryan reciprocates that, they need each other. When Aryan gets better, who knows what she's going to do. But at the moment, all she knows is that Aryan is sick, he needs his father to get better, so she decides to protect them both because without each other, both Aryan and Sultan are nothing.
And regarding the whole heroine struggle. I don't think she ever wanted to get into films or anything. If I recall properly, she was pushed into it.
They already showed Madhu being a little acquainted with the movie world as a worker, and she saw part of what RK's life was like. And now she's meeting a Don. Like someone said, what if he becomes her financier in films? They're are so many endless possibilities and I'm excited. They creatives promised a larger than life story, and well so far it definitely has been interesting.
I think a lot of people are thinking of Madhubala as one of those typical love stories where the girl ends up with the guy or she gets separated from the guy, etc. But this is supposed to be something new. So regarding Sultan and Madhu, you can never know if they're gonna be endgame. The CVs have so much to show, as you pointed out. I like to think of Sultan as one part of her life. Before she was born: her life consisted of a tyrant, merciless murderer. Growing up: she lived on the film sets as her father worked there. Adulthood: she got married to and starting loving RK. Now: divorced/ hates RK and helping a Don. Who knows what's going to happen in her life next? All we definitely know about is that she's going to become an actress and RK is going to always be a part of her life.
Her story, and I'd like to remind people that this show is about Madhu, hence the show's name, has so many parts to it and we only know a little bit for now. RK is just a part of her story, just like Sultan and Aryan and the countless other people who will enter it sometime in the future.