Boyfriend says my heart wants you, but my brain says we are not the best fit. what does this mean?

My bf and I are both in our early 20s, recent college grads in a large urban city, and have been dating over two years. Recently, he said, "My heart wants you, but my brain says we do not have a future together." His brain says we are not the best fit for each other, but his heart wants me to be with me. He said the reason he is telling me this because he doesn't want me to be crying hysteria if he decides to break up with me.