Emotional affair

Ladies I need some advice if any of you have gone through any of this my Counciler says my fiancé is having what is the start to a emotional affair with his neighbor. She has a boyfriend but recently my fiancé and her have become closer. Spending a lot of time hanging out at her parents on the weekends and texting eachother everyday. They work together so does her bf and his brother. They see eachother and text eachother every day which is already frustrating. Now he has gone to visit his family and it’s becoming more noticeable this emotional affair. Today he hung up on me to answer her phone call with her parents just asking how he’s doing. They are becoming closer and closer which is breaking my heart. I don’t want to lose him or leave him but I just need to know if any of you went through this too