<human>: Can you give me the gist of the text in a nutshell?

We've been long distance for 3-4 years, met a few times. We agreed we can be in an open exclusive relationship, meaning you can sleep with others, date, but not love love them or let them reduce the quality or quantity of time spent together.
I'm 25, she's 22. I'm in Canada, she's in the States.

So she met this guy online 8 years ago, and never met him until today. He's 36, lives 1000 miles away. His mom ratted him to the cops for weed possession so he got in jail for a month and when he got out his mom essentially kicked him out of his house. So he messages my girl and he's like: "Well i have nowhere to go, would you like to meet me" so he does that. I'm really sketched out. He claims he's thinking about where to stay, what state to move to.

My girlfriend is highly promiscuous, lonely and very trusting, so they're fucking and when she talks to me about him her voice shows feelings for him. I'm really annoyed because i don't think this is a good idea, and i told her why, and to be careful and not to give him money. He's basically staying at a hotel for the past week and they spend the day together after her work. We have good communication and she's honest with me. So yeah, sketched out by this guy, even though she claims he is a nice guy and that she's been chatting with him for years. 

Also I'm at a loss how to remain her primary lover. I told her to tell whoever she dates that she's in a relationship with me, i haven't asked her if she told this guy yet. Is it a reasonable thing to ask, or is it a good way to go about it?
<bot>: What can i do when my significant other is getting involved with a red flag person? How to structure an open relationship in a way that allows her to see other people, but not be replaced as her favorite lover?