Detox reactions including nausea are very common. Perhaps if your BF replaces the oil more often and is very sure not to swallow he can continue. He probably need to do some work on his liver and colon, and especially his diet if a gentle detox like oil pulling causes problems. If he is that toxic, he is wide open to any number of serious health problems. Look at the nausea as a sign something has to change with his lifestyle.