What should you do if your friend is unconcerned but not on purpose??

I used to work with the best friend,and we have shared the happy time together.But recently I found him unconcerned to almost all of my behavior in peacetime.for example,he didn't care my question;when I started a conversation,he responded with few words and even just a smile:somtimes he looked all around instead of facing me.But I know he still like me,which could be observed by what he did during my difficult period.And i learned that's just about his character from his other friends.Maybe he just only donn't know how to keep a friendship.But I was really disappointed and hurt about that.Once I wanted to talk about this,I was afraid that maybe hurt his feelings and even distroy our friendship.And there may be some unusual sense between us when we on a conversation after that. Well,what should I do?I need any advices.