Although the 35-year-old lothario owns bachelor pads in Montana and Los Angeles' San Fernando Valley, he has scheduled meetings with estate agents so he and Katy, 28, can get their own place together.
A source told People magazine: ''He always insisted he needed his own place to make music but clearly that's changed. Now he mostly hangs out at Katy's place in LA.''
While the duo were initially reluctant to go public with their relationship, they are now serious and want the work to know.
The insider added: ''They've both acted very private about their relationship in the past but they seem comfortable about going public with their relationship now. They seem very happy.''
John is so serious about Katy he is even rumoured to be planning to pop the question after just six months of dating.
A friend of the musician said: ''John really likes the fact that Katy is so independent and not needy and clingy like the other girls he's dated. This is the first time John's felt so strongly about a girl. She's played her cards perfectly.
''They really do bring out the best in each other. It wouldn't surprise me at all if he proposed.''
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