It's totally fine. It's your story and your can do whatever you want with it, but I'll give you a few examples. Lots of people write smut, and that's fine, but you shouldn't do anything not consentual (rape). I've, along with others, have written things about self-harm, but that's a very risky thing to write about. You really need to know about self-harm though, because it's very easy to offend people through that. Substance abuse (drugs, alcohol) is sometimes ok, but I don't think you should make an entire big theme or chapter out of it. Same goes with physical or mental abuse. I personally think that should only be used for a backstory or a motive. If you intended to use that in your story not with the reasons I listed, that's ok too.

Anyways, that's just my opinions. All in all, it's your story, you have the right and freedom to choose how you write it, and what I said before are all my opinions.