Stormarksgothi,

Which Norse god or goddess is associated with marriage?

The primary goddess associated with marriage is Frigga, associated with marriage, childbirth, motherhood and the home.

There are others, often considered aspects of Frigga (though I accept them as separate entities) including Var, the goddess of marriage vows (and responsible for punishing those who break them), Sjofn - who inspires love in humans, and Lofn - who brings together those whose love is prohibited.