<human>: Can you succinctly summarize the text in 1-3 sentences?

Length of relationship: 5 years

My fiancee, let's call her L, and I have known each other for 7 years, and we've been dating for 5. We recently got engaged (the wedding is a month away), and I thought things were going well until I overheard a conversation between her and her mother, C, where she told her that she no longer loved me and was thinking of leaving me for another man. I didn't say anything at the time because I wanted to talk to her alone. I trust L, and she has never given me any reason in the past to doubt her faithfulness.  

I have a well paying job, at a bank, and she has just started her own computer business. We've been living together for the last 3 years, surrounded by our circle of close friends, and she is especially close with my best friend, M. We've even discussed starting a family in the future, and we've unofficially "adopted" a young orphaned neighbour, D.  

I don't know why she would be unhappy with our relationship. I provide for her, I give her financial support, I love her so much.
<bot>: I think my fiancee is cheating on me, maybe with my best friend, I don't know what to do because this is tearing me apart.