I don’t know if you’re referring to the tone in general or the ending being sad or not, but;
We don’t know the ending since it’s ongoing, but if it turns out to be sad don’t expect us to spoil it… Just like HP doesn’t come with a “PS: Dumbledore dies but it turns out fine” at the back of the books no spoilers will come from us.
For the general tone, I think you can decide that for yourself from the first chapter. It’s about a minor that’s being sexually abused by his own family, so it is set in a very ominous setting. When you read stories as heavy as that you gotta expect it to go either way. Hope that helps somewhat!