My cancer boyfriend is distancing & acting cold?

We've been going out, but for over a week he just started acting cold and really distant. He wont talk to me for days and when he sees me around, just doesn't acknowledge me. In the begining he was really keen and we would talk for atleast 20 hours a day. now it's nothing. He also keeps alot from me. When i tell him other guys flirt with me or ask me out, he just doesnt care. I texted him just now if he's feeling better but he just goes he's "busy". Is this in their nature? Do they act extremely cold & distant and then after back to normal? How long will their mood last because this is gone on for over a week. What do I do, just sit back & wait patiently? Im worried if I do, he's going to distance even more. Do i wait for him to initiate the convo first? If you don't believe in astrology, then just think of it in a normal perspective please. His birthday's on June 29th.