This is something he can’t help himself with. The fact that he is attracted to you is making him want to be around you and to have a certain level of intimacy.
While you’re talking, he will lean in to hear you better and he will lower his voice so you have to lean in too.
It’s something he does unconsciously, because his body is totally in control when he’s around you.
He will also touch you accidentally, like touch your shoulder when he’s talking to you, move a hair from your face and touch your arm.
It’s also a great opportunity for him to see how you will react to his touches.
If you pull back, he will too. But if you do nothing or even touch him back, it could encourage him enough to finally make a move.