Help: feeling like a stuck up

I know this may seems ridiculous but lately in my relationship I've seen my boyfriend act more childish and irresponsible (he's 17 but he seemed so mature at the start)

He spent a paycheck that he promised that would be used to get me gifts and instead bought a expensive phone to replace his perfectly okay iPhone because it starting making him mad. (I pay gas constantly, any good or drink while we're out, I just want a gift that ain't a pair of earbuds that break within a week)

Then he spent his paycheck on GTA and wanted to spend more so he asked if I could wait again to get my gifts and I said no, which he respected but spending close to $100 on GTA? It's ridiculous.

I love him and don't want to break up with him, any advice on how to make him...less juvenile?