Affleck and Lopez were photographed together in Montana. A source tells ET that the two have "natural chemistry" when they're together.
"They have a good time when they're hanging out and things have been easy, fun and exciting between them," the source says. "They've stayed in touch over the years, so the two of them reconnecting isn't a huge surprise to their friends. Ben is protective over J.Lo and they're trying to be as low key as possible."
According to E! News, the two vacationed together alone at the Yellowstone Club in Montana for a week. Meanwhile, a source tells People, "[Jennifer] spent several days with Ben out of town. They have a strong connection. It's all been quick and intense, but Jennifer is happy."
"J.Lo makes it a point to have cordial relationships, especially with Marc, since he is the father of her children," a source previously told ET.
Meanwhile, while Affleck may have been hanging out with his ex-fiancée over Mother's Day weekend, he did give a shout-out to his ex-wife, 49-year-old Jennifer Garner, on Mother's Day. The two share three children together -- 15-year-old daughter Violet, 12-year-old daughter Seraphina and 9-year-old son Samuel.
"So happy to share these kids with you," he wrote on Instagram alongside throwback pictures of Garner with their kids. "Luckiest parents in the world. Thanks for all the good you do. Happy Mother's Day. Love, their Dad."