There must be someone you know who is pretty knowledgeable about computers. Start by asking them how to delete files. Have them explain how to delete your email history and delete your cookies (especially if you were surfing the net for sex toys or day-use locations).
If your spouse shows up at your job unexpectedly, make it short and sweet and get them out of the office quickly, without raising suspicion. Your spouse could easily pick up on a vibe by noticing something as simple as an exchanged smile between you and your co-worker/lover. Your lover may even confront your spouse with a look of triumph, possession or guilt.