I texted my boyfriend that we broke up, and he never texted me back.

One is that he wants to treat it coldly and looks at your follow-up reaction coldly. He uses static braking, which shows that this person's mind is still deep. The other is that he doesn't know how to face such a thing. He is considering whether to break up or how to make you change your mind. And he thinks it's okay to break up. So now that you mention it, you can only face the reality.