Kate Upton has been sending mixed messages to men and women worldwide. In a minute, she’s smitten with "Dancing with the Stars Pro Maksim Chmerkovskiy, then a minute later she’s single. But after a short-lived romance with the DWTS judge, it looked like the Sports Illustrated model is single again.

A source has revealed that Upton and Chmerkovskiy have called it quits after six months together. Here are the top reasons for the couple's short-lived romance:

1. Age Difference

The DWTS pro is 12 years older than the curvy model. Chmerkovskiy is 33 and Upton is 21 when they met early this year. They shortly got involved romantically in June 2012. After months of on-and-off rumors that they were hooking up, they finally admitted seeing each other in August 2013. It was the model's 21st birthday when the rumors came to life as the former couple got snapped together to celebrate. They were seen together in many dinner dates shortly after. They were seen holding hands and getting cozy as they strolled the streets of New York and Los Angeles.

“The fact of the matter is that she is a 21-year-old girl and Maks is 33,” an insider said in an interview with New York Daily News.

2. Different Priorities

Things are a bit difficult for the former lovers in terms of their schedules. UPI.com noted that the couple were really in good terms but the time they spend apart must have “killed the romance.”

"They are really good friends still and speak all the time, but their schedules just made it too difficult and it fell apart," an insider was quoted as telling Us Weekly by UPI.com. "[Chmerkovskiy] has a lot of respect for her, but it just wasn't working anymore."

3. Kate Got Serious Quickly

Things apparently got serious for Upton after she celebrated her 21st birthday with the DWTS judge. It will be recalled that the couple created a buzz in August when they were spotted dining together to celebrate her birthday. This was followed by more dinner dates and leisurely walks with their hands glued to each other. Things appeared to have gotten more serious when their respective families came into the picture.

“She liked him and brought him to meet her parents at a football game. She invited him to a lot of family things. She got serious about him quickly, and he thinks she’s a good person. It just didn’t work,” the source said, according to the NYDN.

4. Maksim May Have Panicked?

This, however, may have caused Chmerkovskiy to panic. The source who spoke to the NYDN noted that the DWTS pro may have felt discomfort when Upton thought it would be best to find a place where she could get closer to her man. The source suspected that Chmerkovskiy may have been alarmed when Upton had gone apartment-hunting in Flatiron District, in Manhattan, New York at arm’s length from the guy's place in Fort Lee, New Jersey.

5. Long Distance Killed the Romance

Tehran Chronicle noted that things began to “fizzle” in September 2013. “Things actually fizzled out between them in September,” a source said, according to Tehran Chronicle, explaining Chmerkovskiy’s move to Tinseltown to find his stars not on the dance floor but in the big screen.

“Maks moved to L.A. for his acting career and Kate relocated to NYC. After that, they actually didn’t see very much of each other. There’s no hard feelings, I’m sure they’ll remain friendly,” the source added.

A friend of Upton told the NYDN that they “were never that serious in the first place,” but pointed out the distance indeed caused the split.

“It was the distance. He travels and she travels, and it didn’t work out,” Upton's friend said, according to NYDN.

It should be noted however, that it was the same time when Upton declared she was single in an interview for Elle’s September 2013 issue.

Was it really the distance? Or Chmerkovskiy just did not appreciate Upton claiming no one has her heart.

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