How will having anterior cruciate ligament injury affect my long-term health?

Depends on multiple: Anyone with a cruciate injuriy responds differently depending on a lot of factors, like age activity/demand levels; athletic status overall and specifically the status and shape of the quadriceps and hamstring muscles and also concurrent injury to other knee structures.

Unknown: The real answer depends on many factors. The long term affects of a knee that is acl deficient is one of a higher probability of damage to cartilage (the tissue lining the ends of your bones), meniscal tears (cushion pad between two bones in your knee) and even an increased risk of arthritis.