Sources say the couple, after dating for a few months, spent Christmas together.
And not only that.... Katy, 28, is bringing Mayer, 35, home to her parents!
Katy even sent out this pic on Twitter with the caption, "Santa Baby."
"They're happy together and with her family for the holidays,"
says the source.
"John really likes getting to know Katy's family better."
The source add that the couple are also getting serious about their relationship...
"They've spent a lot of time together and really enjoy each other's company...John is entirely focused on Katy."
As for recent tabloid reports that Mayer has been flirting with other women and that Perry discovered text messages on his phone, the source says, ..
"That is absolutely not true. John would never do that to her, and Katy really trusts John."