How can I make conversation with my best friend and stop it from being awkward?

I am 13 years old, and I have lots of great, chatty friends who I have no problem talking to and laughing with, but when I'm with one of my best friends, David, it is really awkward, and we barley talk to each other in school. If we are walking down the corridor, we won't walk together and we won't talk at all, which makes me feel really bad like he doesn't like me, because he talks to my other friends just fine and it is just with me that he turns quiet. Part of the problem is the fact that I don't want to speak in case he will think that I'm a loser and judge me, but then I think, what if he is thinking that as well, and we don't talk to each other because we think that the other person will judge? As I said, he has no problem talking to anyone else, and when I am sat next to him, and he leans over to talk to someone else (because of the awkwardness), it makes me feel really bad like he doesn't want to talk to me. Despite all of this, there are times (it's usually about once or twice a day), where for a long period of time, I will make him laugh really hard, and he will tap me on the shoulder and talk to me as though nothing is wrong. I know that the way to make him talk to me is to be funny, but I cannot do it all of the time, so when I'm not and he doesn't talk to me, my confidence takes a blow and I must work to make him laugh again. Does anyone have any tips on how to make interesting conversation between two 13 year old best friends and stop it being awkward, and also how to get him to talk to me again? Thanks a lot for answering!