If you try your best to save the marriage, you won't be forced into any "gotcha!" scenes where Anna is conquered by another man. I know people would argue Anna sending sexy pics is being forced into cheating, but I disagree, and besides, you don't even know or have yet to determine how Anna responded to sending those pics... maybe she hated doing it. That's for you to decide
. I like David and Anna, and if you want to save their marriage, I'm cool with that and want to see it happen, so there's a path.
I will warn though - if you make some bad choices - that could backfire. Just like in real life, choices have an impact and you can't control the results. If NTR scares someone so much, I'd tell them just to avoid this game. I think the choices will be fairly obvious though.