"Mad Men" actor Jon Hamm has been dating his actress/screen writer girlfriend, Jennifer Westfeldt, since 1997, but it appears that their relationship is going south.

Allegedly, Westfeldt gave Hamm an ultimatum: if he didn't marry her, she threatened to leave him.

"Jennifer's at a stage in her life when she wants stability, security and a family. So she worked up the nerve and told Jon it was time to get married or she was moving on," a source told The National Enquirer. 

Unfortunately for her, Hamm does not forsee a wedding in their future.

"He said, 'If you want to get married, go right ahead. There's the door. Go find someone else to marry because it's not going to be me! '" the source said. 

Westfeldt is very upset about the whole incident, but the couple continues to share a house together. However, Hamm's successful acting career has caused him to have a wandering eye. 

"Jon's like a kid in a candy store these days, and he made it clear that he doesn't want the party to end," the source said. "Jennifer backed down, but now she's miserable."

Westfeldt said that their relationship has, at times, been bumpy. "Relationships take work," Westfeldt told The Huffington Post in June. "You don't take each other for granted."

She also said she doesn't only love Hamm for his good looks, but for his kindness and sense of humor. 

"He's the funniest person I know," she said. "He's the sweetest guy I know. He's brilliant. He's my best friend."

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