How does a guy threat to break up when the other party has already walked away anyway?

I became so frustrated with my boyfriend because he just seems unwilling to communicate about things that are negative or uncomfortable. I reached a point where I didn't care anymore. I didn't care if I ever spoke to him again because it didn't seem worth being in a relationship with someone that wasn't going to communicate with me. I went 2 days without speaking to him. He called me multiple times and I wouldn't answer. He finally left a message saying to please let things go until we could talk in person because if I kept giving him the silent treatment then something serious was going to happen with us.