How could God harden someone’s heart so quickly?

Over the past 2 months I got to know an amazing Christian guy and I seriously thought he was the one for me. He had told me he fell in love with me, he told me Jesus had shown him my heart, he told me that he had a lot of faith in me. All of these feelings went out the window after a disagreement we had. I had expressed to him some concerns and doubts I had and he didn’t take it well at all. He became very stressed and frustrated with me and he decided he didn’t want to talk to me anymore. I tried to reach out to him and I even sent him a long paragraph, completely owning up to everything I did wrong and sincerely apologizing. He just ignored me. I don’t understand. How could someone who was showing me so much care and wanted to grow with me just give up on me? Why does it seem like his heart was hardened towards me and that he doesn’t want to forgive me?