Unfortunately, you cannot control what her friend does or says regarding your W's fantasy. That is why it is really important for you to be hands off, on this.
It is possible that your W will blame YOU, regardless. If your W's friend name drops you in convo with your W, regarding tat-boy, your W will STILL blame you.
Keep yourself distanced in regards to tat-boy and have no convo regarding tat-boy with anyone except here and possibly an IC (that your W is not privy of). Work yourself through this concern of yours, independent of working on the M.
Thing is, there are likely few people who do not have any romantic fantasies. Just that people would not generally act on them or speak them out loud. Once the fantasy is over, it is over and really has no bearing on the M.
My stbx had very definite fantasies regarding a young gas jockey about 4 years ago. I don't know how deep that fantasy was, but it certainly was there. Eventually, that fantasy ended. I have no idea if she dreamt of sleeping with said (teen) gas jockey and it really does not matter. Would not have mattered, even if we would have stayed M.
It is her fantasy that is likely to blow up in her face. Keep letting it go and work on yourself.
