Damn your cock is tiny!

A modern socially monogamous married couple who have always been like best friends while retaining individuality.
He knows all aspects of his life with her are fulfilled & is happy being completely monogamous.
She too appeared to be likewise yet he knew sexually she needed more.
He is comfortable acknowledging his small penis and accepting that size does matter to her.
Great communication = solutions (asymmetric open relationship), she could then embrace her sociosexuality and have fulfilling sex with other better-endowed men while her hubbie remains sexually monogamous.