How should i handle this situation?

soo there's this girl name Daphne who's always flirting with my boyfriend and its getting really annoying..we stopped texting lke 3 hrs ago...usually i dont sweat..but then i look on his facebook page and he was having a flirtatious convo with Daphne that was almost like 75 comments long and it happened 3 hrs ago which leads me to think he stopped talking to me to talk to Daphne -___-...she's always on his facebook and always on his (excuse my language). she even said that she'd kiss him and that they should hook up sometime and all this other bullshit...what should i do? how do i get her to back the hell off?