@SP - Its a kiss and tell - something the tabloids are not unfamiliar with :)
Given the heightened public sensitivity to stories relating to scandal, and the Leveson enquiry, I would imagine the Mirrors editors and lawyers have made some assessment of the validity of the story. From the story, they gave this guy an opportunity to comment, and he refused - so they cannot be accused of at least attempting to get the other side of the story.
Given his comments about the definition and sanctity of marriage, assuming the story is essentially correct, then yes, he would be considered a hypocrite. Tories always get into trouble over sex - John Majors family values campaign and the subsequent outing of Mellor, Yeo et al?