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And I think your friend knows how bad her relationship is and how much of a terrible boyfriend "Jake" is.
So she's telling you all of these things about "Alex" and trying to put you off "Alex", because she's jealous of you and his relationship.
(sounds to me like she might have her eye on him as a back up from the behavior you've described but that's not how it works)
She is not your friend, and Jake is displaying some creepy psychopathic tendencies.
Get Alex and never visit them again.