Someone flirting with my boyfriend

There is a woman flirting with my boyfriend, her kids and mine go to the same school so we see her.

She flirts with my boyfriend, she blows kisses, asked him for a 3 some, told him he is sexy. She knows FULL well he is with me!

My boyfriend gives her dirty looks whenever she does anything.

Now to clarify I am NOT looking for an answer that results in violence! Just some advice or anything as it’s making me really angry!