Why do some straight couples seem to have an issue with their s/o having a friend of the opposite sex?

In my opinion insecurity is a sign of a relationship that is not where it should be..
And I would date a bisexual guy in a heartbeat :-)
I've always wanted a woman who was into that!

FORREAL THOUGH!!! My ex had only female friends and I only have male friends, so we understood each other.

To me it has always spoken to insecurity and control issues, just silly

Insecurity in themselves or lack of trust in their partner (neither is good)