I've lost contanct with my boyfriend the past few days?

My boyfriend and I usually talk each night on the phone. We have been together for a year and a half. I usually call him sometime before I go to sleep. He used to call me every night or nearly every night. I was texting with him during the day on Wednesday, and in the middle of our conversation he stopped responding, so I let it be. I was hoping for him to call me that night, but he didn't. I would call him, but I feel like I'm bothering him. He didn't call/text me yesterday or today either, and I have sort of been waiting for him to. I didn't really want to talk to him about it but I don't want him to call me just because I ask him to. I want him to call me because he wants to talk to me. I just don't want to pester him about it, but I feel sort of avoided. We are having no problems in our relationship, so why won't he call me?