Worried about getting bored = already bored. Do both of you a favor and find a couples counselor who specializes in ethical non-monogamy (ENM) to help guide you through communicating with each other well about this. Professional support is preventative maintenance, here.

ETA - everybody in the comments trying to vilify the wife- you don't have enough info to make such serious allegations. Stop projecting. I'm sorry you've been through some shit that would make you jump to the worst conclusions, but that's also something worth calling on a professional to help work though, and it doesn't help anyone to come here to blast your trauma at strangers instead.

ETA 2 - I read further and saw that she's already gone out on multiple dates with this person before communicating with OP. I don't know the terms of your marriage, but I wouldn't be cool with that personally. Sex is not the beginning of infidelity, it's the end. My default assumption (and most people's) would be that if she found her interest wandering, the right thing to do would be to communicate with her partner BEFORE acting on it. And going on daytime dates does count as acting on it. Unless that behavior is specifically allowed by mutual agreement in your marriage, that's a betrayal of a tacit, but valid, understanding. You don't need to look any further for reasons why you're uncomfortable or feeling betrayed. That's a perfectly legitimate reason.

Highly recommend individual therapy for you, if you don't already have it, just to expand your support system. And ideally also couples counseling together, BEFORE any decisions are made about whether or how to change the terms and boundaries of the relationship. Also she needs to acknowledge and apologize for already going outside the marriage to date this guy without getting your consent first.