Please talk to your vet....he might need some temporary trannies, or maybe be encouraged to use another window to view the world.
Animal behaviourists can be very helpful too - please look into that.
Worst case - maybe rehome him to a friend who has a 2nd floor apt or something. Please keep us posted!
"When I think of Mick Jagger still singing that he can't get any satisfaction in over forty years of being in the Rolling Stones, I have to conclude that he's either lying or not all that bright." -- Henry Rollins