Actually, I kind of liked it in a weird way. It kinds of makes her a more interesting character.
Yeah I agree that Ekta messed up by separating Sammy and Suhani. To be honest though, their relationship wasn't developed that well either tho. Like they hated each other and then suddenly they love each other. I think part of the reason it became so great as it did, was because the characters looked good together and it was the cliche bad guy and good girl pair.
And I thought the Kush and Suhani thing was sweet. But Ekta Kaul didn't really sell the fact that Suhani really loved Kush. I still felt that she liked Sammy more but her pride was stopping her from going back, that along with maybe a debt she felt to Kush because he helped her unconditionally when no one else did.
As for why she killed him...hmm.
I think maybe she was actually get really used to being with Kush and having him appreciate her. Her and Kush kind of did have the perfect life going on. He doted on her and her unborn child and she had her own clinic running well. And plus she was finally getting a mother's love from Priya. With Sammy back in her life, he threatened her perfect family life. It was clear that Sammy wouldn't have stopped at anything to get back into Suhani's life. He was crazy about her. He would've divorced Pihu which would've made Priya go towards Pihu and less toward Suhani. And wouldn't have let her live peacefully with Kush. He probably would've started custody drama and stuff just to mess with them, etc. So she killed him rather than face her perfect life falling apart.
I mean, even though Ram is in jail, her life isn't so bad. Kush still loves and dotes on her. Same with Priya. Even though both are also super busy trying to find the murderer.