Dobby is a good house elf except he isn't. A good house elf that is. For a good house elf are enslaved and happily so and Dobby isn't either of this things.
He is no longer treated like vermin by his family, the Malfoys that are no longer his family, and he is bad house elf to happily be free of them. He has a new and kind master though the good and kind (too kind, Dobby the bad elf thought but never admitted outloud for a elf is to follow their master's words never have opinions nor questions and Dobby, the bad elf he is, does have these things) Harry Potter refuses to be referred to as Dobby's master.
Dobby had thought it was because Harry was raised by muggles instead of wizards so he hadn't been raised in their wizarding ways. Now, Dobby grimly understands and Dobby is not pleased at this revelation. The house elf was not pleased the least bit at his savior's relatives treatment of the too good and kind Harry Potter. Dobby was... ill at ease (Yes! That was the word.) as well.
(Harry, being the kind wizard he was, had allowed Dobby to borrow the neglected books on the bookshelf along with Harry's clothes if the house elf gave his word to never been seen or heard by the Dursleys. One of the books was a dictionary and oh did Dobby love to educate himself to better as much as he loved wearing mix matched socks.)
Dobby knew of obscurus despite the wizarding world's shame of them. The only reason why Dobby knew so was because his former master had been interested in the subject. Or, rather Dobby realized, the power of such a parasitical creature those poor abused wizards and witches had become. It was sad fate for there was no cure for obscurus; no cure for Dobby's Harry if such a fate befell the young wizard.
No, Dobby thought strongly and perhaps even fiercely. Such a terrible fate would not befell the good and kind Harry Potter who had improved the lives of house elves after defeating He-Who-Shall-Not-Be-Named.
'Tis part of the house elf's enslavement was keeping the secrets, scandals, and silence for their masters but Dobby was no longer Lucius' house elf. He was Harry Potter's and happily so! He would inform his Harry what might befall him before freeing the young wizard from his relatives that were just as monstrous as the Malfoys. Then Dobby would be a good house elf once again.
Unfortunately that plan didn't happen with the arrival of Aunt Marge.