I agree with the views of everyone who has already commented. You don't know who you are dealing with when it is only online. Psychopath is a possibility but so are many other ones, including him being a very needy or controlling person. He could have a personality disorder or have a criminal intent. If he's suggesting marriage already that is a very bad sign. It really is... a giant red flag. Try to get your friend to ask herself what kind of person would do that and get out of the online relationship.