Hate to burst your bubble but according to the link you supplied, they in fact do not mate for life (always).

Cardinal Relationships: Bonded, but not Always for Life

Male and female cardinals don’t necessarily mate for life. Although pairs may stay together for multiple years, they do sometimes seek out new mates. One study of a cardinal population in Ohio found that 20 percent of pairs separated during the breeding season and 10 percent more split up over the winter.