Dianna Agron splits from 'Gossip Girl's' Sebastian Stan

"Glee" actress Dianna Agron has been linked to Sebastian Stan -- of "Gossip Girl" and "Captain America: The First Avenger" fame -- since about May, but the couple has called it quits, Us reports.

Why couldn't these two crazy kids make it work?

One source suggests that Agron was "super jealous" of women who Stan works with. "She was always worried that he was cheating on her while he was away filming," the source says, "But he never would."

The NY Post agrees that the long distance was too much to handle -- Agron lives in Los Angeles, where she films "Glee," and Stan's home base is in New York City. "Long distance wasn't working," a source says. "Dianna's coming to New York for Christmas with her mom, so they might rekindle the flame."

Agron began dating Stan after a rather nasty public split with her "I Am Number Four" co-star Alex Pettyfer. Stan has previously been linked to "Gossip Girl's" Leighton Meester.