boyfriend shuts down when I cry

Recently I've been noticing that if I cry around my boyfriend, he just shuts down and wants nothing to do with me. It's a very confusing and sad feeling because I just want to be comforted and work things out with him in the most loving way possible, without an argument. But he closes up, goes home, and doesn't talk to me for the rest of the night... ☹️ I never end up finding out what was going through his head. What does it even mean...