Be discreet

Keeping it secret
Get rid of any proof you've been cheating (bank statements, texts and emails, the smell of cologne on your clothes, etc) and don't go confessing your sins to all and sundry. The fewer people who know, the better. You can never be too sure, and you don't want to make your friends and family feel uncomfortable around your partner by telling them.

Fixing boundaries
However wonderfully handy your house is, never ever invite your lover round for a quickie after work. A marital bed is particularly sacred. Did you know that one of the first questions someone who has been cheated on always asks is 'Did he come to the house and did you sleep with him in our bed?' Aside from that, it's vital for your sanity to keep certain parts of your life separate from the rest.