I used to have very long hair too. I had to get the split ends cut so they would not travel up the hair shaft.
Have you tried any of the oil treatments you leave in for a few hours and then wash out?
Olive oil can be used that way, too, not as expensive as hair products. You put the oil on your hair and wrap your head in a hot towel ( or maybe hot and wet, I am not sure), then wash it out. You could Google then exact method.
Other: Are you getting enough oil (Omega 3's, not the saturated kind) in your diet? Is your skin dry, too? And are you shampooing too often, maybe?
I'm assuming you don't color your hair. I did that once, when mine was long, and it was awfully dried and ruined the hair.