"It has been less than two weeks so it is new again," an insider tells Us of the couple.
"They were still talking during the break," added another source. "When he was done with Nightcrawler he was spending a lot of time by himself and with his family over the holidays and he missed her."
Us exclusively broke news in early January that Gyllenhaal, 33, and the model had split after nearly six months of dating. "They fizzled out. It happened a while ago -- before the holidays," an insider told Us at the time.
Another added: "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. Then the distance just really got to them."
The hunk and Miller, 24, began dating in June 2013 after meeting at a gym in NYC.