This is your relationship so obviously you get to decide what's inexcusable behavior from your SO. Do you view him leaving those comments as a form of cheating? 

Are they all from a year ago or were there more recent ones?

Not trying to make excuses for the guy, but maybe he genuinely didn't find tattoos attractive until he saw the style/placement of that redditor's tatt. A person's personal tastes can change over time.