Can Katy Perry tame perpetual heartbreaker John Mayer?

The pop star, 28, who has been casually dating the "Shadow Days" singer, 35, "believes she can change him," a source says in the new issue of Us Weekly (out now). "She doesn't want to be just another one of his conquests." (Mayer's exes include Jennifer Aniston, Jessica Simpson, Taylor Swift, Jennifer Love Hewitt and Minka Kelly.)

Part of Perry's plan, according to the source, is playing hard to get. "She recently told John she was open to see other people," the source reveals. According to a second insider, "Once Katy turned her back on him, he started chasing her again!"

For more details and the couple's hot and and cold romance, watch this week's Hot Stuff video, as explained by Us Weekly senior editor Ian Drew and special guests Hi-Fashion, whose Sprechen Sie Hi Fashion? EP is available now.

Also in the roundup: Pippa Middleton cancels five TV interviews, Sean Penn thinks ex-wife Madonna is still "so hot," Dancing With the Stars eliminee Drew Lachey blasts Bristol Palin, and much more!