The duo decided to part ways because Perry felt their respective work commitments gave less time to spend with each other.
"The main thing which led to her split with Russell was spending the majority of her marriage to him on tour and she said dating Rob felt like being with Russell all over again," showbizspy.com quoted a source as saying.
"It's a shame as they both liked each other but Katy wants to be able to have a relationship with someone she isn't constantly having to work out what time zone they're in. Rob was gutted but Katy said she didn't want to get in too deep and then break his heart so it was best to cut things off before they got serious," the source added.
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