Ouch. Wait until he tries something else and just record him. She's not going to believe her 'best friend' is a psychopath without clear evidence. Get that and you'll be rid of him. He'll probably try scaring you off every time her back is turned so you'll have plenty of opportunity. If she decides to keep him after seeing the evidence then run, dude, run...

It’s not creepy to be a nice guy or a friend. But it’s very creepy to pretend to be that in order to try to get into a sexual relationship with someone… I agree that the best thing to do is to record Mr Creepy’s comments if you can and play them back for GF. If that’s not possible you can at least tell her what he said - That ought to open her eyes so she can see for herself if he seems a bit off. Frankly it seems odd that Creepy would actually tell you what he did when keeping his mouth shut would have likely allowed him more latitude in his plan. I guess he watched too many James Bond villains.

Reality is going to dropkick that guy in the face. The chances of a girl suddenly realizing that her friend is "the one" is basically nil.