<human>: I need some really fast, good advice.  My sister-in-law called me and said she found a message in her other inbox on facebook, from March, that said her husband (my brother) answered a craigslist add for gay sex?????  and he didn't want "silly" business going on in a marriage?  The guy had a VERY GRAPHIC picture showing my brothers face and included his phone number.  

How do I confront my brother about this?? My sister-in-law wants me to come over in a hour to discuss some options and shes hurt and doesn't want her marriage to be over.  They dated since they were 17.  She is afraid my brother will try to gaslight her and that is why she wants me to be involved.  

I am also going to remove any of his guns from the house before we confront him.  I love my brother.  He is the most like me and we don't even talk to the rest of our family because we had a real fucked up child hood.  I don't want to lose my relationship with him either, but what the fuck...how can he hide this from everyone if its true?  What else can he be hiding?

Summarize the given text in a few sentences.
<bot>: Sister-in-law got a message from a stranger on facebook in her other box and had a very graphic picture of my brother answering a M4M ad on craigslist.