Lois Lane in the Rain

There’s this girl who’s been friends with my fiancee for a couple years, and he used to like her. That doesn’t bug me, but here’s the thing: She’s outright told him she doesn’t like him, yet, whenever he’s in a relationship she always tries to break them up and (even if SHE’S taken) texts him in the middle of the night saying she misses him and asking him to go drinking with her and hook up after at her place, etc (which he never does, obviously). BUT as soon as he’s single again, she completely dumps him. She doesn’t talk to him, she dates other guys, she acts like he’s not good enough to talk to her. She even tells her friends he’s too fat/ugly for her to date.

She obviously just likes the attention.

I talked to him about it, and he realized what she was doing, he got mad and stopped talking to her. But just now they’ve started talking again. It seems pretty innocent (and honestly he’s sooo oblivious he has no idea if a girl is flirting with him).

What do I do?