["I am reluctant to confront my my best friend's girlfriend. I think my best friend is cheating on her...", 'You should definitely first talk to your friend and clear out the concerns with him before talking to his partner', "I don't know what to do but I'm apprehensive. Should I tell her?"]
As I said, first ask your friend why is he behaving in such an unacceptable way
I am reluctant to confront my my best friend's girlfriend. I think my best friend is cheating on her...