You're over-thinking it. He's gone to a bigger club, in a higher division, and this next bit is the clincher, for a (much) bigger salary.
I know it's hard for us supporters to understand but footballers, managers, coaches, agents would sell their grannies for a few bob more. They are mercenaries. They wear your badge, not for love, but for money.
View them as they view you.
Don't overthink it. It will drive you bat**** crazy.