What is the explanation for this contradiction: a young man proposed to me then withdrew after consulting some sheikhs, claiming a desire to devote himself to his religion, even though he used to say that marriage is half of one's faith?

Allah decreed your sustenance before your creation, and this includes marriage or its absence. So trust in your Lord and increase your supplication and obedience. There is no blame upon a Muslim woman for seeking marriage from a righteous man, as some female Companions did so. Or her guardian may offer her to a righteous man, as Umar (may Allah be pleased with him) did with his daughter Hafsa. A man's aversion to marriage might be good for you, for Allah decrees nothing but good for a believer. Righteous men are many, so do not tie yourself to one man.