You don't believe that living together before marriage = fornication?
Are you implying that Jesus may very well have sinned?
As for Jesus never dating, marrying, fornicating, etc... and being a model... for a unbeliever, no He could never be a role model...
But, for those born of the Spirit... most certainly He is a role model. One must be born-again though.
Since when did we start talking about weddings? Weddings are not necessarily what constitutes legal marriage. Certainly now, in America, weddings are not necessary at all... a simple trip to the court for a marriage license, couple of questions from the JOP and signatures and two are legally married. If the couple want to have a big church wedding, or a destination wedding, whatever...but no one is married legally until and unless they get the license and sign it witnessed by a legally recognized officiant.
What the Bible does show specific examples of is that marriage was more than just living together... marriage involved going to the bride's family, having them recognize the union, usually involved a dowry of some sorts... and the community recognized it as a legal marriage as opposed to the woman being the man's concubine.
Concubines are the biblical example of people living together without marriage. Concubines had limited legal rights, but were in no way considered wives. God never instituted the practice of keeping concubines, just as He didn't institute the practice of divorce. The New Testament has no provision for the practice of keeping a concubine within the Church... none. The New Testament only recognizes marriage, only refers to a husband and a wife (one man/one woman), and we are told to keep the marriage bed holy. There is no mention anywhere in the New Testament of any man being able to have more than one wife or keep concubines. There is, however, many mentions regarding marriage as being between one man and one woman. Had the practice of polygamy and keeping concubines been widely accepted within the New Testament, surly it would have been referred to, instead of the very pointed references to one man/one woman marriage. "Let each man have his own wife and each woman have her own husband." 1 Corinthians 7:2