"He really fell hard for Michelle, and she wanted to just have fun and not have a super serious relationship. Plus, Michelle is interested more in women than men - so that was an issue as well," said the site's insider.

Case of the Ex?

Prior to the romance-filled summer, Rodriguez made headlines for her same-sex relationship with supermodel Cara Delevingne, 22 after some pretty heavy PDA earlier in the year.

Efron wasn't up to the challenge in terms of competing with the memory of Delevinge. E! Online wrote, "Cara was always being mentioned," said a source.

"Cara would spend time on the same boat and Cara and Michelle have all the same friends. It was just a lot. It was always, 'Cara, Cara, Cara.'"

Such lifestyle and gender preferences weren't a hit with Efron. "As great as it would sound to most guys, Zac didn't want to share her with anyone, especially other women," explained HollywoodLife.com's inside-track.

The two apparently had it out while together in Ibiza, Spain and with Efron having had invested more in the relationship, he's hung up on the actress and "still wants to be with her," reported PerezHilton.

Rodriguez has opened up previously about her sexuality, the first time being last year in October. She told Entertainment Weekly that she's "gone both ways."

"I do as I please. I am too f***ing curious to sit here and not try when I can. Men are intriguing. So are chicks," the Daily Mail UK quoted Rodriguez.

The "Neighbors" actor also had his own highly publicized relationship in the past with co-star Vanessa Hudgens that ended in 2010. During the span of the relationship, nude photos of Hudgens surfaced online - allegedly ones that were meant for the actor.