He probably existed, since the alternative - that people somehow conspired to invent him - is much less plausible. The Bible does not say he was married, which leaves his sex life if any open to speculation; but then it scarcely mentions his siblings either, so perhaps that just wasn't interesting to the writers of the gospels. The life of an itinerant preacher may not have left time for a youngish man to settle down (especially one who thought the end of the world was nigh).