what does it mean when he randomly gets shy

so a boy i’ve known for quite a long time always use to be really confident around me and flirty. i didn’t ever reciprocate it cos i didn’t really like his arrogance i guess, but after some time he kinda grew on me and we started talking for a few months, and now when i see him he’s different. he’s a lot more quiet and awkward and sometimes can’t really look me in the eye. why would he go from cocky n arrogant n flirty to just shy n awkward?