Am I wrong for keeping the money?

I have 2 jobs work 6 days a week and I'm a student. I picked up a couple of dog sitting jobs and I kept the ~$500 to myself. Me and my boyfriend have a joint account and he's upset that I kept the money I got from the dog sitting gig to myself.

A little background... my boyfriend is into cars. So you know what that means. He likes to get car parts and mods that ARE NOT CHEAP and often plans on getting these things before we have the money for it. So when I want something modest like a pair of headphones or to go out with a few friends for drinks the excuse is "we don't have money for that." That's another issue I'll get into on another post but the point is I've felt like I was never able to get anything since the "extra" money we had coming in was always already "spent."

If I kept the money in the joint account the odds of it getting spent within a week are 100%. Am I wrong for just wanting something for myself for once?

Updates
+1 y
So now that I've made this "side money" he doesn't think he should pay towards some bills since I have money for it from what I've made... that doesn't even make since
Am I wrong for keeping the money?
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