Any theories?

Adversary

So I was with my ex for 2 months exactly. Everything moved super fast by his initiative. He said I love you first, and he said he meant it to the bottom of his heart. He kissed me first. He initiated everything. This was the happiest relationship I have ever had. We didn't fight, he was affectionate and so was I. Everything felt great. Friday was awesome, he felt sick but we still talked that night and he asked me if I loved him. I said yes. We both said goodnight and went to bed. I woke up Saturday and he texted me good morning like normal. I felt something in the pit of my stomach... so I asked him to FaceTime and he said sure. Something seemed completely different. I asked what was wrong and he told me he doesn't feel like he was in a relationship. He felt like we were best friends. It's like someone poured cold water down my back. He said he was going to work on it, but I told him "what is there to work on?" So I told him we shouldn't be together if he felt this way. I'm just so confused. He told me he has always meant everything he told me. How can that be true?