I don't know how much sense I am going to make right now, but here goes. I feel that they are using the ADHARNGINI concept here. Every time they end up saving each other, I feel that the writers are highlighting something.
To the uninitiated, ARDHANGINI is the wife. The other half of the same body. If the male body is one half, the other half is the wife, the female body. Together they make one being. ARDHA meaning half and ANGA meaning the body. So ARDHANGINI is the other half of the same body.
Something similar to the concept of the better-half. But that is a western concept and a modern one I feel, that calls the partner the better half. It is mostly used by men to refer to their wives.
In the concept of ARDHANGINI, no one is superior or better, they are equal. We might have our own thoughts about how Indian culture treats women and all but the word itself does not call anyone superior or better. The word indicates equality.
How can one half be better or worse than the other? Both the halves are EQUAL. And one can't function to its fullest extent without the other. Say, the right side and the left side are two halves of my body. Can I say that the right side is better just because I use my right hand to do most work? Does that mean my right side is the better half? No. Because, without the left side, my right side will not function properly. I need my left side to ensure smooth functioning of my right side and vice versa.
Similarly, a man needs his wife to function to his fullest capacity just like a woman is incomplete without her man, in marriage. Individually I feel both are completely independent of each other. But in marriage, each is incomplete without the other.
So I feel the writers, whether knowingly or unknowingly, are highlighting this concept. Bella and Mahir are two halves of the same being. No one is superior or inferior. They are equal.
So that is why they have always shown Bella fall weak in Mahir's absence and vice versa. Bella has been saving Mahir from the start. Today they showed a mere human defying the powerful magical cave and entering just to save his trapped wife.
Whenever one falls weak, the other one takes over. They balance each other. Just like an artist walking on a tight rope leans one way and then the other to keep her balance, the one being named BeHir lean one way and then the other to walk the tight rope called life.
Also, I am sure most of you are aware of Lord Shiva's ARDHANARISHWAR roop? One where he and his wife Devi Parvati merged to form one body with one half being a male body and the other one being a female body.
According to the Wikipedia
Ardhanarishvara represents the synthesis of masculine and feminine energies of the universe (Purusha and Prakriti) and illustrates how Shakti, the female principle of God, is inseparable from (or the same as, according to some interpretations) Shiva, the male principle of God. The union of these principles is exalted as the root and womb of all creation.
So what I feel is this. Since they have shown Bella as a Lord Shiva's devotee right from the beginning, I feel they are trying to indicate towards Lord Shiva's this particular roop. Mahir is the Shiva to Bella's Shakti. They are inseparable from each other.
That is how I feel that whenever Bella is in trouble she prays to Lord Shiva, whom she believes in and Mahir turns up to save her. It has happened even when she hated him. He was always her soul mate, even when she hated him. He was always her other half her ARDHANGA even when she was not ready to accept him.
BeHir will always remain the two halves of the same being.