I believe Luke did have something to do with their separation, tbh. Perhaps Kesha did reach out to Katy once upon a time and she decided to put fame over friendships. Who knows? California Gurls is a bit too much like "TiK ToK" tbh... eh.
I really don't want to think about Katy like that, but I honestly don't see her taking Kesha's side in this, especially when she's not exactly been seen with / talking to Kesha since like 2010/2011 (?) and she's actively STILL collaborating with Lukasz.