I'm sure your wife would view it that way, too, which is why you're not going to tell her. What happens if your wife decides she'd like to have sex with you a week after you've had sex with a? Do you tell her that you can't or that you have to use condoms to avoid putting her health at risk (yes, there are risks beyond HIV, like chlamydia for women is much worse than it is for men who can be silent carriers). You can't assure that someone is "disease free", even if they had an STD screening report from a week before. You're selfish if you don't have an honest conversation with your wife before you have sex outside your marriage.