It expired dude. Clint staff says it's in the rules but it's not clear. After 31 days of purchase your star will expire and will show up again after another purchase. Sucks does'nt it?
The tournament winning star is also a temporary one for seven days after you win.
All Stars are temporary, buying some credits make the stars appears for 31 days.
After my star disapers can i still sell cards to other people