Is your boyfriend cheating if he says he's going out with friends and will be sleeping at his parent's place because he will be home too late?

Not necessarily. Ask where he and his friends are going for the evening and you may just find that it's closer to his parent's place and since there is obviously going to be drinking involved he probably wants to stay close-by. If the place he is going too is closer to where you live then that's a problem and ask him why he can't stay with you. If you've never had a problem with your boyfriend before and he's loyal to you then don't start second-guessing and end up ruining a beautiful relationship. In order to have a good relationship there has to be good communication and trust. Don't forget to ask him where he and his friends are going and you can figure out the rest from there.