The Expat guide to Brussels and visa section is a helpful resource.
I believe that since you don't have citizenship, you will need a Schengen Visa to live in Belgium. Once you qualify and gain citizenship then that is the stage where Schengens are no longer necessary. Some Schengens are easier to get than others, depending on the Country/Embassy. If your partner is British/EU Citizen and you will be travelling with them then the Schengen should be free and expedited (according to EU Law it will, but in practice there's always some catch) , there will be some questions that you don't need to answer on the form, used to be marked with an *. If your partner is not an EU Citizen then all questions and fees apply. The website of the Foreigners Department of the FPS Home Affairs (https://dofi.ibz.be/sites/dvzoe/index.html) is the official site. A recent article on EasyExpat, Obtaining a Visa to Live, Study and Work in the Schengen Area, should be of help as well.

You may also find helpful info from expats already in Beligum though the network or expat blogs.

Let us know what path you choose and about the process. Anyone have tips or information? Best of luck!