I tore my acl over a year ago in highschool i never had surgery but i have full flexibility. how can this be and should i not get it fixed?

ACL deficiency : Although some patients do well, this is rare. Without acl reconstruction you can expect instability particularly with decending stairs or turning quickly from side to side. Long term acl deficiency ultimately will end up with severe osteoarthritis in 15-20 years. In the interim, meniscus tears (cartilage"shock absorbers" in the knee) are more likely.