When did you decide he wasn't just dating you but was your boyfriend? Did he ever say anything along the lines, "let's be boyfriend/girlfriend"? It could just be he likes having someone to date occasionally and has never thought along the lines that you are his "girlfriend" just that he can say, "See, I date, too."

When I was in college there was a guy who asked me on the most wonderful dates (all day canoeing trips with fun groups he belonged to, etc.) but he did it a total of about 3 times in 2 years. He never kissed me or anything but when we were together we had a marvelous time for like 12 hours and enjoyed one another very much! I never figured it out. LOL

I would just casually ask him, next time you're together, maybe in a slightly teasing fashion, why he never likes to chat anymore? See if you can learn anything.