In my opinion there is a difference between an old flame and a new friend. So you're already talking different rules. I would try expressing concern to the spouse first that you're not fond of the friend being "over friendly". Just a simple discussion. If it continues for an extended period of time and you know it's not just joking around, I'd pull the friend off to the side and have a discussion with them about. No threats, just a simple reminder and let him/her know it makes you a little uncomfortable because you can't tell if it's a game or a play. If it just started, it's probably too soon to tell which it is. At least make an effort to figure out on your own if it's just joking or making a move.

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"BOY: On a hot summer night, would you offer your throat to the wolf with the red roses? GIRL: Will he offer me his mouth? BOY: Yes. GIRL: Will he offer me his teeth? BOY: Yes. GIRL: Will he offer me his jaws? BOY: Yes. GIRL: Will he offer me his hunger? BOY: Yes. GIRL: Again, will he offer me his hunger? BOY: Yes! GIRL: Yes. BOY: On a hot summer night, would you offer your throat to the wolf with the red roses? GIRL: Yes. BOY: I bet you say that to all the boys!" -Meatloaf