If you haven't already done so, print the most damning e-mails and save them off-site (maybe with a friend). Or print them to .pdf and e-mail them to yourself at a web-based (like gmail) e-mail account.
Also, begin to DOCUMENT EVERYTHING. Just do a daily journal; it's therapeutic, you can use it to look back on and see what works and what doesn't, and you can also use it legally if it ever comes to that (and it doesn't have to if you don't want it to).
When you get a moment, please give us some details on your financial arrangement: who-makes-what, what joint funds (and joint credit cards) she has access to, etc. Included in this, can you tell me what things she is spending money on that are enabling her affair: cellphone, make-up, gym membership, lingerie, gifts, etc., and who's been paying for them? I'm going to suggest that you immediately end all financial support that directly enables her adultery.
