Whats wrong with my dog?

I'm 13 so i dont know a lot. Ihave a medium sized sheltie (shetland sheepdog) and a large black lab. the lab is 2 and the sheltie is 11. they have fought 3x and every time the lab got laid out by the sheltie. they are aggressive to each other all the time, especially over attention. but, my sheltie keeps lick the inside of the labs ear like hes gonna get beat up by the lab if he doesnt( haha ya right) i hate when they fight. but why does he do that?