SBM. We don't know for sure, but I don't see why she would lie to her best friend about it. I also don't see the friend making it up. If it wasn't true, the police would find out and the friend could be put under suspicion.
I doubt she had multiple suitors at her age, especially if most thought she was still happily married. Perhaps it is more likely that JFG, as a well off bachelor, had several older women interested in him.