Should I be tight lip or say something?

I just need to get this out because somehow it's bugging me. I know it's none of my business but somehow I feel a little affected. I don't expect any of you to have real answers but I would like your opinions. Ok so I have friend, lets call her "Mary", who has been in a relationship with "Josh" for almost 6 years now. I'm not really close to Mary but she is a friend due to me being best friends with her sister. I'm a very close family friend. Just recently I began hanging out with Josh and found him a pretty cool guy. And until recently, Mary has been having a long distance relationship with "Roy". She announces it on facebook that she is no longer with Josh but with Roy and Josh doesn't know about it because he's not computer savvy. Well her sisters were giving her a hard time about it and she's pretty manipulative so she goes off crying to her grandma saying that her sisters were judging her and that her and Josh were no longer together. And being her grandma's favorite, her grandma lectures her sisters (shes a bit ignorant when it comes to Mary's lies).I've confronted her about it too but she says shes doing it because it's payback for when he cheated on her (a long time ago when they were really young like 14 or 15) and because he treats her like crap. ANYWAYS one of Mary's cousins confronted Josh about Roy and when Josh confronted Mary, she started crying and saying that she loves him and that her cousin is a liar. And may I just say that Josh is gullible and ignorant also. Mary still talks to Roy and says "I love you" and just recently bought a webcam to video chat with him and it's like a thorn in my gut. I've come to know Josh and he's a pretty cool guy and though I may not know the whole story of the relationship I don't think it's right that she keeps Josh around like a blind puppy. Josh has history in his family of suicide and depression (his older had hanged himself) and somehow I fear the longer she keeps this charade eventually he will find out and make rash decisions. What should I do? Be quiet and mind my own business or say something?