Lady Kai, welcome to longlocks!  I'm sorry I don't have any advice to give you other than to take your time making a decision about what to do with your hair.
Perhaps consult with a color specialist at a salon? 

Good luck!

Bitte

Liebe daughter_of_fire,

I see fata morgana   has already given you some great tips about how you might try and lighten your color and get the henna out step by step, but don’t forget to test any coloring before you put it on you whole head. Some people do that by picking a single lock of the hair still on their head, but I’d recommend collecting hair from your brush or comb for a couple of days, the more the better and then try the dye on that. If your patient and collected enough you can even try out different dyes or how long to leave the dye in.

As far as I know split ends and dry hair isn’t the worst thing to worry about, but for your hair to turn green.   That is why hair experts always tell people to wait till all the henna has grown out until they try to lighten their hair with chemical dyes, some components can turn henna dyed hair a sea-ish, green. So make sure you test any dye before you put it on your head, and to take a look at your test results outside in natural light, because I have seen women whose hair looked perfectly normal inside, but once the sun hit it you could see the green shine through  (Something which can also happen to natural blonds if they use the wrong, industrially treated kind of henna  )

Hey, fata morgana, am I reading this right? I’m not the only one who experienced their hair becoming dryer after using henna? Because I always thought, everyone told me how good it was supposed to be for my hair, why has no one ever mentioned it dries it up, too? In fact, that was the reason I came on today, to check for conditions you guys would recommend, so I don’t have to cut it short again…

Wow, thank you for the tips, feta Morgana! I’m quite happy with the very natural-looking Redhead the henna turned me into from the Natural Blonde I was before, so I’m not thinking about going back. But yeah, the fact that my hair dried up like that after everyone told me how good henna was supposed to be for your hair made me think and now I know I’m not the only one

I’ll definitely try the Nivea on my hair, that honestly something I have never thought of before. So far all I’ve put in over night was coconut or almond oil, but that the lotion might actually be easier for my hair to absorb is something that never occurred to me before.  

I have to say, though, I don’t like Wella much… I had trouble using it before, itchy scalp and all that. I prefer Redken, ‘specially the Butter Treat stuff. But it’s very expensive here in Germany otherwise I’d be using it every day
And yeah, you’re right, although we have some of H&M’s make-up and hair products in Germany I have never seen hair dye being sold here But I do like their strawberry mask for hair… it makes my hair look like I blow-dried it and then used hairspray to keep it looking fresh, even though I did neither! Love that!
I wish they were selling the dye here, too

But, yeah, the problem is, like daughter_of_fire said, the problem isn’t really to go from henna to dark, it’s to go from henna to blond… tough nut to crack, no matter how much to moister… it might still turn green. Well I hope it turned out ok for daughter_of_fire, but I can say I don’t feel the need to go back to blond. It’s true, more boys might be hitting on you, but they’re not necessarily the kind of guys I’m interested to see, of you know what I mean