"They fizzled out. It happened a while ago -- before the holidays," one insider tells Us. "He's back on the scene." (Lainey Gossip posted a story speculating Gyllenhaal's now-confirmed single status on Tuesday afternoon.)
"Things were really good between Jake and Alyssa right up until he had to leave for L.A. to go shoot a movie [Nightcrawler] in the fall," adds another source. "Then the distance just really got to them."
Indeed, the handsome actor, 33, has been busy filming upcoming thriller, Nightcrawler, in which he plays a struggling, freelance crime reporter who comes across the underground world of L.A. Another source tells Us that Gyllenhaal "was very taken with [Miller], but I think their work definitely drew them apart."
The big chill occurred before the holiday season. "They were apart for the holidays, and things weren't good with them even before that," a source says. "She's very much a long-term relationship girl. He's not as much of that mindset."
24-year-old Miller opened up to Us in late October about her relationship with the hunk. "Things are good," she said then. (As Us Weekly exclusively revealed, the couple started dating in June after they first met at their gym.)
Gyllenhaal has a long history of dating gorgeous stars: His exes include Taylor Swift, whom he briefly dated in late 2010, Kirsten Dunst, his girlfriend from 2002 to 2004, and Reese Witherspoon, his last longterm relationship, which ended in 2009. "I know people are bummed, because many thought he had a chance this time," an insider tells Us of the actor's latest split.