Some "innocent" pastor?? Believe me, any pastor who's "been in the business" for even a few years has seen sin in all kinds of forms! And "shacking-up" is probably the most common type of public, manifest sin we have to deal with these days.
Pastors see it all, understand the depths of human depravity better than anyone, and so we're not shocked by anything.
“Partner” just screams out “homosexual.” I don’t think any normal shacking up people use it.