I'm not familiar with your situation, but you should talk to an atty about this, if you haven't already done so. You should continue to meet the family's NEEDS, but have no obligation to meet her WANTS (unless and until a judge orders it, as perhaps being "the lifestyle to which she is accustomed," which -- sadly -- women often get, even when they've been unfaithful to their husbands).
And you DAMNED sure aren't under any obligation to enable her affair financially.
I would suggest that you do this IN WRITING, and run it by someone first, to make sure you have it out there in black-and-white that you will continue to meet your obligations, so that she doesn't twist it around on you.
