I see no option for "the appropriate ending." I think it's easy to say a happy ending, but sometimes a story needs to end on a sad note.
Joss Whedon says that he doesn't give viewers what they want, but what they need, because the viewer or reader will almost always select something that will make them momentarily happy ... and will ultimately damage the work.
There was a book that hit big last summer, and all of a sudden it seemed like everyone was reading it. It got a lot of praise, but also got dinged on the ending. The ending made sense to me given the tone of the book, and the psychology of the characters, but readers wanted, oh, justice.
Which leads to the unfair part -- the right ending can sometimes be the one that is unpopular and makes people angry.

Joss Whedon still gets grief for giving viewers what they need -- what they
painfully need. (But I truly think your book is better off in the long run as long as your tone was honest and hinted heartbreak was a possibility.)