Sorry for not commenting in German - I don't think my German is good enough.
'cativar' would be 'to capture' or maybe 'to tame' (translation used in the English edition of 'le petit prince') - not 'to do'. Translating it like that would lose all poetry that was there. It means that if you capture something or someone, if you bind it to you, that makes you responsible for what happens to them.
Also, wouldn't this sentence sound better if you change the word order? (Du bist ewig verantwortlich für das, was du getan hast.)
Yes, I think that sounds good. 'cativar' (itself of course from a translated version of the book) is something like capture. Not sure what the French original of the book uses here.