"God-given Marriage" emphasizes a kind of God-given, especially beautiful fate. This word is usually used to describe the ideal and well-matched situation between two people, such as lovers and lovers.
"Love is like oxygen" emphasizes a couple, that is, an excellent partner. This word is usually used to describe the harmony and perfection between two people, not only lovers or lovers, but also friends and partners.
Generally speaking, if you describe the relationship between lovers and couples, both can be used. If you want to describe other types of relationships, perhaps "love is like oxygen" is more appropriate. But this is not absolute, and it may also depend on your personal preferences and context.