You push harder. Eventually the cabinet breaks away and starts accelerating. But you have to keep on pushing just to keep it moving with a constant velocity. When you stop pushing, it quickly slows down and comes to rest. When it is moving with constant velocity, the two forces exactly cancel.
Frictional forces are intermolecular forces.
These forces act between the molecules of two different surfaces that are in close contact with each other. On a microscopic scale, most surfaces are rough. Even surfaces that look perfectly smooth to the naked eye show many projections and dents under a microscope. The intermolecular forces are strongest where these projections and dents interlock resulting in close contact. The component of the intermolecular force normal to the surfaces provides the normal force which prevents objects from passing through each other and the component parallel to the surface is responsible for the frictional force.