Married

This is a page consisting of evidence supporting that:

Steve Purcell's wedding toppers

screenshot of Sam & Max at the alter in the recap section of the first episode of the cartoon

Confirmation from Steve Purcell

While limited to Sam's imagination, this shows that Sam put thought into proposing to Max.

Valentines day drawing by Steve Purcell

Max referring to Sam as a first lady

An answer from the Reddit AMA on July 8, 2021

When asked about his dating life, Sam responds "Don't tell anyone but I'm kind of off the market right now."