My Girlfriend

She's 19,been with her two years but she met a man, like older man around 40. He's done something to her, now she goes see him nearly every night. When she gets back always tiered. Only thing she told me that he's a good man, his friends too. So I'm sure now that she goes with him and his friends so now there's a bunch of 40 year old using my girlfriend like a dolly. I can't do anything. My mind has been playing with me making me think of those men taking her at the same time and in my head it's crazy, I imagine one behind her, one in her mouth and one in each hand, that's four men at the same time and she must like it she keeps going back there. What am I supposed to do? My girlfriend is just so you*g and already they turn her into a se* machine. Shit.