is he cheating?

i have a rel gut feeling my boyfriend is cheating and it driving me crazy.  he has become very distant. doesnt kiss me or hug me. and i cant acually remember the last time we had real intimate sex.  i know this part dont sound like a big deal but, he always through the day texts me on his breaks and stuff. now he barely tet me back at all. if not at all.  and the other night he went to pick up his sister from work, baring in mind he was just ment to pick her up and take her home. it doesnt take that long probably about an 1hour. well he say i see u in a bit babe. so im like yeah ok. 1hour and a half to 2 hours later he comes home. so i had a go and said where have you been it doesnt take that long, he says I DONT HAVE TO TELL YOU EVEYTHING I DO. any way after an arguement and i calmed down he says that he stayed at his sisters for a coffee. so i said you know you dont have to ask my permission to do that, but it would be nice if you could have text me to let me know u be a bit longer.  he has also got an arsey attitude to me like he came home from work the other night and said IM OUT FRIDAY NIGHT! GOING OUT WITH THE MATES FROM WORK! i did have a go because there was no need to be so arset with me.  i really am getting fed up with his attitude. and the feeling that he is cheating is getting stronger. if he is i really dont want to know. coz i can not stand liars or cheaters. if he has or is cheating thats it i will walk away,  im even finding myself now trying to detach my self from him incase he decides he wants out or that he is cheating so that it makes it easier for me to walk away.  am i being stupid. or over reacting or do u think maybe im reading to much into it.  im making myself ill over this. i cant eat sleep and im so stressed over this.  i dont know what to do??  HELP!!!!!!!!!!!!!!!!!!!!!