Can't keep henna hair open because it gets tangled. Recommendations?

Hey! I dyed my hair with henna (Light Mountain) a few months ago, before that I only used chemical hair dye for years. My hair is very long (100cm) and probably damaged and the second I try a open hair style, it gets tangled pretty bad.. :( It is not the hennas fault, it was the same beforehand.

How can I keep it manageable, is there any sort of oil which doesn't prevent the henna from sticking to the hair the next time I try to dye it?

I condition with apple vinegar once a month and used aloe vera gel and flax seed gel but it didn't help enough. Help?