Fiancee's bossom friend alleges infidelity

He loves his babe so much, and trusts her as he should.
They've been on a long distance relationship, she visited three months ago.
He's engaged her and is making plans to have her as wife.
Last week, an unmarried very close female friend of hers calls him about his fiancee, implicitly suggesting infidelity
Although she had had a qaurrel with his fiancee, yet she painted a complex picture with some of the threads of info accurate
Guy trusts his babe, but is haunted, hurt, harrassed by some of the classified info he had shared with his babe.
Could the fiancee's girl friend be mischevious, could everything be woven around real facts the babes had shared in the past?
Has had his fiancee's version of the story but many questions seem to compel attention
Guys, please help out... what should he do?