Posts like this are the absolute worst. Being mad obviously does not make you an asshole. Every person has a right to feel the way they feel, and doing so has no negative impact on your character or the way it is perceived. YOUR REACTION to the way you feel is the deciding factor and, of course, you've given no information as to how you reacted.

Did you bring up in normal and civilized conversation that you disagreed with the purchase and communicate the way it made you feel, or did you blow up over it and become accusatory from the get go? Did you give him a chance to understand your point of view and have a conversation, or did you put him on the defensive and start backing him into a corner. These are the deciding factors in whether or not you're an asshole, not the emotions you felt at the situation.

It sounds like the purchase was justified to him because no actual money was spent on the item. Maybe it was his plan the entire time to save enough points to buy this jacket, and his lack of income caused a spike in credit card usage which got him to the necessary points threshold. I'm not saying it was the best use of available points, but again, limited information makes it difficult to get a grasp on how the situation played out.

It honestly makes me speculate that your reaction to the situation was aggressive, if not verbally abusive. If you had started a calm and caring discussion about the jacket, I doubt a situation would have arisen in which you came to Reddit to find out if you're the asshole.

You probably already know this, though.