Don't be afraid, if he is really your best friend this shouldn't ruin you friendship.
I don't think this is the right time, though - quite the opposite. Wait until you live closer to him if that's anytime soon, and for his mom to get better. Be a good friend meanwhile. 
Another thing on your mind is how to tell him. There are many ways you can go about this. Two of which are:
1. You tell him early on. If he doesn't feel the same way you cut your losses early.
2. You wait until you get even closer to him and perhaps his feelings develop for you to the point where he has to tell you/show you how he feels and becomes transparent. At the same time, if he doesn't develop those feelings for you, you're at a greater loss. 
Now you have to decide - how much are you willing to sacrifice?
				
			 
			
		 
			
				
			
			
				"Don't worry about the world coming to an end today. It's already tomorrow in Australia"