Is it permissible to take out a loan to complete a marriage in order to stop watching pornography and masturbating, or is this considered forbidden usury?

It is not permissible to watch pornographic films. Whoever engages in such acts must fear Allah and abstain from them. The Prophet (peace be upon him) guided young people to marry if they are able, and for those who are not able, they should fast, for it curbs desire and instills piety. One should avoid the causes that lead to watching prohibited things, such as solitude and browsing stimulating websites, and instead occupy oneself with truth and righteous deeds. Marriage may not require a lot of money, and approaching usury to complete a marriage is a greater sin than looking at what is forbidden. This is one of the tricks of Satan, who calls to indecency, while Allah promises forgiveness and grace.