Justin Bieber and Sofia Richie’s relationship has fizzled, and they’re moving on to see other people … TMZ has learned.

Sources connected to them tell us Justin and Sofia were never all that serious to begin with — despite vacationing together in Mexico for her 18th birthday. They haven’t been seen together in public since then, and we’re told they haven’t been talking much lately.

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Neither seems too busted up about the breakup. Sofia was out Sunday night at The Nice Guy, and also at a treats! Magazine party over the weekend … enjoying herself with friends. We’re told Justin is single and ready to date other girls.

In other words — exactly what you’d expect from an 18-year-old and a 22-year-old.
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