Yes, a lot of men do look at internet pornography. But is it justified? No. Is the future wife being too sensitive? Absolutely not. As a wife, the woman has the right to expect good behavior, including loyalty and fidelity, from her husband. Is it possible for the woman's fiance to mend his ways? Yes. Will he automatically stop looking at porn once he gets married? Probably not. As women, we shouldn't be naive. Internet porn is accessible 24 hours a day and is highly addictive. It is pretty hard for a man to automatically kick his porn habit. In all likelihood, she'll end up putting up with his problem until he finally decides to kick it himself. So now she has to decide if she can live with this type of weakness in her husband.
If the answer is no, then it is probably best if the woman calls the marriage off. Even if she puts a "no-porn" clause in your contract, it won't stop her husband from looking at it. And then she'll be in a situation where she has the constant threat of divorce looming over her head. Such an atmosphere of tension probably won't resolve the situation. This woman needs to be very up front with the brother [in Islam, i.e., her future husband]. If he doesn't care about guarding his eyes from what is unlawful, then why should she marry him? If he won't take serious steps to fight his habit, then she might not want to get into this situation. No one wants to be constantly suspicious of their (sic) husband.