You should have a hobby e-mail account that you don't access directly on your phone but only through the web. There's also a terrific app for iPhone and I wonder if it's available for Android -- "My Secret Apps" installs itself as "My Apps" and holds photos, videos, contacts, notes, a web browser and so on. You have two different PINs on it, your usual PIN that your wife probably knows that opens the app looking like there's nothing in it, like it's never been used, it's just sitting there for nothing. Then there's a different PIN that opens to all your information. It probably wouldn't fool LE but it should be enough to fool your wife.
Above all be careful! Delete contacts from your normal contacts list and recent incriminating phone numbers and texts, as well as recent destinations from your GPS.
Lots of guys swear by burner phones but I don't because a second phone would only raise questions; my wife would never believe I have a second phone for work. If you have a burner phone make it inaccessible but don't keep it a secret; it will raise a huge amount of suspicion if she finds out about it and you haven't told her.
Also be really nice to everyone, especially her. Don't get into other illegal or addictive stuff. Be the kind of guy that everyone would say of, "no I don't believe he would do something like that. Not him!"
Be careful, be scrupulous, and THINK. The consequences of getting caught are huge.