“Mad Men” actor Jon Hamm and actress Jennifer Westfeldt saddened fans when they announced their breakup Monday, but they did not provide a reason for it. It left fans speculating about the cause and previously dismantled cheating rumors surfaced once more. However, it might have had something to do with Westfeldt being tired of taking care of the actor, who is recovering drug-and-alcohol addiction, Entertainment Tonight said in an exclusive report Tuesday.

"She wanted him to grow up … and he never wanted to," a source told ET. "She was tired of being his mother."

"Jon and Jennifer really fought hard to make their relationship work, Jennifer more so than Jon," the source added. "They were together for many years, but in the end, it was too much work. It's no secret that Jon likes to go out and leads a very party-heavy lifestyle. And Jennifer was just tired of that."

A different source claimed arguments caused the breakup. "They've been fighting for a while, but now they're done,” an insider close to Westfeldt told Us Weekly Monday. “They decided to finally split. It's sad."

Hamm, 44, completed a 30-day stint in rehab in March. Fans were shocked when the news broke since a public statement had not been made about him seeking help for drug-and-alcohol addiction.

Part of it could be because he likes to keep his life private. "I understand it constitutes news these days, but it’s between me and my family and not something for public consumption,” he told TV Week about going to rehab.

Neither Hamm nor Westfeldt, 45, has spoken out publicly since the initial joint statement. "With great sadness, we have decided to separate, after 18 years of love and shared history," the former couple told People Monday. "We will continue to be supportive of each other in every way possible moving forward."

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