I have an immigration question that's not worthy of it's own post so I'm gonna randomly throw it here in case anyone feels generous.

I have a friend whose girlfriend is Russian. She was in the states on a student visa and her visa couldn't be renewed because, well, she's Russian. They are likely to get married and her inability to be in the states accelerated that timeline. He admits there's a thought in the back of his head she's using him for citizenship, but he doesn't believe you can fake the level of chemistry they have. He's financially stable in his mid-30s and experienced in the dating world, so he's not a loser who is falling for the first girl to screw him or anything like that.

Let's say she is using him. What are his legal liabilities if he's been conned?