1999 Honda Civic blue exhaust smoke and burning oil?

1999 Honda Civic D15 72k mileage engine is loosing oil after a lengthy drive and also noticed smoke from exhaust, think it is blue. Have a full aftermarket exhaust system with decat on too, could decat be the reason for smoke?

No, the exhaust system you have installed has nothing whatsoever to do with it burning oil. Blue smoke is indeed a symptom of oil burning. Why is is burning oil? Because the engine has been neglected or mistreated and the rings are worn. More than likely it had been run to death. You can destroy any engine if you mistreat it or neglect regular oil/filter changes. The only fix is a complete engine overhaul. Unless it is using lots of oil and smoking badly just keep driving and adding oil as necessary.