No. Does he have his son full time or can you only stay on nights he isn't there? That would be my heartfelt best suggestion. I wouldn't stay the night anymore when his son is over.
This is not ok. I am unsure why this question would even be asked. If a 7.5 yr old crawled into bed with me, I am an adult and I am naked... First response is not let the child crawl into bed. If that was unavoidable, I would cover myself and remove the child in order to become decent. Then tell my bf to maybe lay in bed with his child out of respect. Then again honestly, if I had a boyfriend/husband whom had a child with me or even outside of our relationship I wouldn't lay naked.
Tell the kid not to do it.