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.
A wife is Islamically required to keep good marital relationship with her husband in the same manner that he is required to do so; Allaah Says (what means): {And due to them [i.e. the wives] is similar to what is expected to them, according to what is reasonable.}[Quran 2:228]
Among her having good marital relationship with her husband, is beautifying herself for him and being keen on pleasing him as much as possible. Indeed, this is one of the best acts of getting closer to Allaah and a way of getting the affection of the husband and making peace and tranquility prevail in the family, and so, she will obtain the best of this world and the Hereafter. For more benefit, please refer to Fataawa 89964 and 85308.
Therefore, we advise you to continue advising your wife and you should have a mutual understanding with her on the basis of being keen on achieving what would lead to the stability of the family and avoiding dissension. Then, if she improves, all praise be to Allaah, otherwise you may keep her and marry a second wife if you are able to fulfill your obligations of spending on both of them and being just to both of them. For more benefit about the right of a husband to marry a second wife without seeking the permission of his first wife, please refer to Fataawa 85948 and 84411.
As regards divorcing her, it might not always be the best solution, so you should not resort to it until you think it over carefully and balance between keeping your wife and divorcing her.
With regard to what you mentioned about thinking to go to prostitutes, then this is whispers from the devil so that you would lose this world and the Hereafter by doing so. Therefore, you should absolutely avoid thinking about this and avoid any means that could lead to it.
Concerning oral sex from both the husband and the wife, then you should avoid it and the wife is not obligated to obey her husband if he asks her to do this for him as this contradicts the noble etiquettes and good moral character and it is contrary to the Fitrah (natural disposition upon which Allaah created mankind) as well.
Also, oral sex could lead to touching the impurity and touching an impurity without necessity is forbidden. Allaah Says (what means): {Indeed, Allaah loves those who are constantly repentant and loves those who purify themselves.}[Quran 2:222]; which means those who stay away from dirty and filthy things.
Allaah Knows best.