POE WHAT IS SAFE?

At the point of Entry I always believe in answering all the question truthfully, so anything they ask I answer as honestly as I can.

My bf is finally going to come to visit me, what should he say? Would it be safe to say he is visiting his GF for the summer before he starts school? Background of my bf is he has been a PR of the USA for over 20 years, he just apply for the Re-entry permit so he would be allow to visit. Would it be safe for him to say he is visiting his gf? Should he just say hes on Vacation? If they ask where he is staying he should just give them my address and say I am his gf?? He will stay here for two months, until he starts school, would that be a good enough answer. What are most reason for for denial @ POE??