My friend's boyfriend is totally scamming her. Is she really that dumb?

She is extremely gullible and believes everything he says. One of the many b.s. things he tells her is that he is a "private eye". I actually know one, so I asked her to check if he was legitimate and licensed, and no he is not. I told my friend this, she told her boyfriend, and now he forbids her to see me again and he's sticking to his story! WTF? Did I really just lose a friend over trying to expose a liar? It would be so easy for her to verify this. She only needs to ask him where he works, ask him for his license number.....DUH. Do I really have to stand by and do nothing?