What is the ruling on borrowing from an investment bank with 5.8% interest to be repaid over five years, and is this considered usury (riba), especially when necessary for marriage and housing expenses?

This loan is usurious and impermissible because it involves a loan that draws a benefit, which is the usury of Jahiliyyah forbidden by the Quran and Sunnah (definition). Those who engage in it are cursed by the tongue of the Messenger of Allah, peace and blessings be upon him. Your need for marriage or building a home is not a necessity that permits dealing with what is unlawful.