Boyfriend who acts like a teenager?

I’m about to have a baby with this “child” age 20. And I’m 21. He wants to do all the cutesy high school shit like matching lock screens matching this and that. And toxic high school relationship things like checking each others phones. Not trusting me whatsoever. I’m full grown women with a baby on the way. He’s a high school dropout. What do I do? This is so annoying? Advice? Tips?
Boyfriend who acts like a teenager?
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