Not hardly the same. One is a marriage, one is resume padding. But, not sure what this has to do with atheism. I think the man marrying for his career is an amoral ass whether he belives in God or not. Likewise, the marriage for love, is a marriage whether or not the couple has a belief in god.
Then you're changing your argument. Before, you were trying to argue that an act is intrinsically moral, irrespective of motivation. But here, you're arguing that the same act can be moral or immoral, depending on motivation.
The Christian has no such tension. Motivation matters. And as I've developed at some length, the greatest and all-overriding moral imperative is love for God. It trumps everything else, or taints it by its absence.
Dan