We all knew Katy Perry and John Mayer were getting serious -- but who knew they were getting serious so fast? Sources say that John Mayer have already popped the question to Perry ... and he didn't get the response he'd hoped for.

Grazia (via Entertainment Wise) reports that Mayer is so determined to show his love for Perry that he may have actually scared her off a little bit. My, how the tables have turned!

A source said, "John won’t run from Katy again. He knows his bad-boy reputation and what happened with Russell hurt Katy, and he'll do whatever it takes to show he's the one she should marry."

However, Perry "doesn't feel ready" for another trip down the aisle so soon. "John's proposal really unnerved Katy," an insider revealed. "Even though they have discussed it, she thought it was too soon. John was gutted."

The source continued, "Katy loves John, but doesn't feel she has had enough healing time since her divorce. She told him she just needed a bit more time to feel whole in herself again."

You love who you love, but you can't help when you love them. Give it time, John -- we bet she'll come around!