Anorexia?? best friend?? help plz?

ok so sorry but its a long story. in 6th grade i became friends with my now current best friend. his parents are hella strict if he got anything below an A he was a failure in his eyes. he had to be the best at everything. his parents even pushed him to be the best athlete and in health class in 9th grade he watched a video that said all good athletes have 5% body fat and something clicked and he worked towards that. he brought it down to 3% and passed out during class one day. he thinks theres nothing wrong with him and he continues to do it. he did get better for about a year but then relapsed after him n his gf broke up. i'm just trying to get a better understand and learn what he's going thru, and how i can help. cuz our friendship is on the rocks cuz i can't keep watching himself do this. i just can't but i still got his back and am will be there for my best friend. thanx for any info and advice