Nothing worse than feeling violated. If she had unprotected sex with you after not using a condom and not disclosing that fact, she took away your autonomy over your body and consent. Both of those are very hurtful and dismissive of your feelings and you as a person. Add that you had an agreement (or was it a rule?), and she lied to you on top of that... The hurt stacks up.
For the most part, it seems to be a general consensus that rules to control others do not work. A rule is used to control other's behavior sometimes, to make someone feel safe or special, etc. An agreement is something that's discussed and all parties commit to. Many times someone will say "Everyone needs to use condoms with others" and assume everyone agrees, but in reality there wasn't agreement, it is just assumed that it was agreed upon because it was said and nobody said "no." That's a rule.
Even agreements can be broken. The question is, how do you handle it?
You are in a pickle because you read her texts, which is also a violation. You'll both need to own what you did and try to work past both transgressions to deal with the heart of the issue... You had an agreement (rule) that doesn't work and needs to be renegotiated. You can assume she won't magically start using condoms with him. So, what now? Maybe you need to use them with her for your own health and safety. Maybe, if the relationship with BF is established and testing is done, you might feel more comfortable. Maybe if he consents, she could share his safety practices which you might feel more comfortable with.
She's your wife and you trust her. Chances are she made her decision based on info you aren't privy to. She sees and talks to him regularly and has built a comfort that you might have too, if you had the same relationship with him. It's just that you don't know him, how he dates, tests, etc., and that unknown makes you uncomfortable.
Maybe you don't bring up that you saw her texts. Maybe you just have a check-in over current agreements and if they need modification. See if she says yes and initiates changes.
You could confront her with a gotcha, but that's rarely helpful and you'll have to out yourself, as well. Both of you hiding what you did isn't the best policy, but if she comes clean during the renegotiation and you do too, it will go a long way towards healing that broken trust, because instead of fighting about it, you found a solution instead. She will learn that she can come to you if something is not working and you'll feel more confident she will work with you in the future, instead of doing things behind your back.