How do you know if a guy likes you ?

ok there this guy i really lke and i don't know if he likes me he always try and makes me laugh and he does make me laugh but i think he got a girlfriend he doesn't really mention her much and today he gave me a sig and at work he always does the jobs am supposed to do he says you don't have to do it i will if you want but i need to do if he likes me were the same age both 17 does anyone no what a guy is like around you if he likes you please help me i think i like him tooo xx