Why is he acting like this?

Ok, so my boyfriend has been acting really weird lately. I thought it was just a phase and he would get over it, but alas it reappears. He starts acting really moody and then when asked what is wrong, he acts like it's nothing. It feels like he is trying to push me away while making it seem like it's my fault. I really don't see why he would be acting like this. He keeps saying stuff like, "you never take initiative," and, "I'm just tired of everything." I need a little help with this. I am so stressed out.