Maybe you met a love rat who just wanted to fall in love with you and didn't want to take the final responsibility for you. This kind of love rat is the most common one in society now, and it has only one purpose. First, praise you with sweet words, turn you into his girlfriend, try every means to get close to you after you become his girlfriend, and finally just want to trick you into bed and have sex with him.
If it is the kind of person who is particularly scum, after getting your body, he will never be decisive to you again. But this time, this love rat has always maintained this relationship with you, so that he can always get you personally. But if you propose to get married, he will never agree and will not give you that ownership.
Or, it is possible that he really loves you, but he is a person who is afraid of getting married. He is willing to love you, be responsible for you, and be with you all his life. But because of his fear of marriage, he can't break through this psychological barrier and marry you.