She isn’t in love with her friend. In truth, she’s probably feeling lust toward her friend. Her friend likely gives her the attention she craves, makes her feel seen and desired, and perhaps even offers those intimate moments that fade to black. I’m not saying you’re not doing any of those things, but that might be what’s happening. It could evolve into love, yet the real question remains. The best possible outcome for both of you would be a good one you’ll see. Most likely, it will stay private between them. The bad outcome is watching them dote on each other while you receive no affection from your wife. You become just a checking account. The worst outcome is being ridiculed, put down for wanting your wife, left feeling disrespected, uncared for, and unloved.
Only you truly know the situation and the women involved. Have a conversation and see how it feels. Fight for your relationship to stay monogamous, or cut your losses and start a new life. Think about how it will affect your child or children. I don’t know their genders, but that can play a role. I’ll say there are many possible ups, but also many possible downs. Don’t dwell on the negative or write yourself off; the answer is always no unless you ask. And be sure to set clear ground rules. You don’t want to be in a loveless, fade‑to‑black‑less relationship.
