Guys, why do u always hide your chest?

the guy i like usually talks to me/ fixes his hair when he sees me, but lately he's been seeming depressed. like he wont really talk or laugh anymore. and whenever he sees me, idk y he does this but he crosses his arms over his chest and sometimes fixes his hair. the movement is very jerky/abrupt. and also he does not seem very relaxed anymore. like he is always tensing up and wont stretch back anymore if i am near while he is doing it he jerks away immediately. guys y do u do this? Im just wondering about the noticeably jerky movements and stuff. its getting kinda odd. thx