All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
We will summarize our answer to your questions in the following points:
1- There are religious texts that prove the permissibility of each spouse to lie to the other, and this is not peculiar only to the husband with his wife. Moreover, the scholars stated that what is meant here is the lie by which a religious benefit is achieved and the affection between the two spouses is increased, and provided that this does not lead one spouse to be unjust to another. However, some scholars stated that what is meant here is what is known by Tawriyah (saying something which has more than one meaning and intending a meaning different from what the listener is likely to understand). In any case, it does not mean the absolute permission of lying.
2- Looking at non-Mahram women on the pretext that one is looking for a second wife is nothing but deceiving one’s own self, before it is considered as deceiving his wife, because Allaah does not permit something that could lead the dissolute people to achieve their desires. Rather, Islam permits a man to look at a woman whom he wants to get engaged to and wishes that she will accept to be his wife if he proposes to her, and is prepared to marry her if he likes her and she agrees to marry him; so these conditions should be met. Jaabir ibn ‘Abdullaah narrated that the Prophet said: "If one of you proposes to a woman to marry her, then if he can look at what incites him to marry her, then he should do so." [Abu Daawood] The scholars said: 'This means if he wants to propose to her.' For more benefit, please refer to Fatwa 91413.
3- Flirting with non-Mahram women and establishing a friendly relationship with them is absolutely forbidden, and such an act is not permissible whether or not it is in order to get engaged with a woman. Indeed, such sins may lead to some conflicts in marital life. Allaah Says (what means): {And whatever strikes you of disaster — it is for what your hands have earned; but He pardons much.}[Quran 42:30] For more benefit, please refer to Fatwa 119267.
4- It is not permissible for each spouse to lie to the other in order to do what incurs the Wrath of Allaah.
5- It is not correct to say that if a wife does a mistake, her husband should divorce her immediately; rather, in Islamic Law, divorce is the last solution and there are steps that should be taken before resorting to divorce in case the wife is disobedient; for more benefit, please refer to Fatwa 85402. Similarly, in Islamic Law, it is permissible for a woman to ask for divorce is she is harmed by staying with her husband. Nonetheless, the Islamic Law advises both spouses not to hasten and to seek the means of reconciliation because Allaah Says (what means): {… and settlement is best.}[Quran 4:128]
Allaah Knows best.