The fact of the matter is you can't convince a man to be in a relationship with you. He has to feel it and words won't make him feel it for you. Maybe he just got scared, who knows, but when a man says he doesn't want a relationship with you, for the moment, you have to believe him. The more you question, convince, bargain, the further away you will push him.
It's a good chance that he felt smothered, or he felt you were getting too serious too fast. Maybe you were acting too much like a girlfriend before he was ready. Men like a challenge. If he was coming on strong and you just fell right into the role of couple hood, his challenge may have ended too soon and he became bored.
The last man to tell me he didn't want a relationship with me I believed him. How you react to this can determine if he will or will not come back around. If you hold on tighter, he is not going to ever be yours. When I was told that, I was prepared. I felt the distance before hand. I replied in agreement, not what he expected. He expected drama.
When a man says he doesn't want a relationship, agree with him. Tell him that you understand, he can't help what he does or doesn't feel. Yes, you are disappointed, but you deserve a man who does know what he wants and a man who is able to be in a relationship with you. Thank him for his honesty and letting you go to find what you deserve, then shut him down. Go no contact.
This will get his attention. Men are used to women trying to fix it, not a woman who is taking care of her own heart. His respect for you will shoot through the roof. I know this is hard, but it's the only way to get his attention, do the unpredictable. Let him walk away, and you do the same with feminine grace.