As Baldeee already explained, "unless" is correct. It's possible to build a sentence with "except," but it's rather awkward: "I will not forgive you, except if you apologize." This is correct grammar, but you will probably never hear anyone talk or write that way. Baldeee explained that correctly. We use "belong" more often in other types of statements. A very common form is, "I belong in Los Angeles. It's too cold up here in Seattle."