Let me be real here.
Its your story not mines.or anyone else.
B) Its a fictional story, not mine, yours.
Whether or not not is okay hinges on one question.
What are you trying to accomplish?
In my opinion the word romanticize X has lost so much meaning I'm growing to despise seeing it and my eyes glazes over it. But here you go.
If your point is to write a tragedy and the plot has believable characters then honestly just go for it, That ending that ending is more a cautionary tale than anything else.
If your are writing a very dark messed up I would say watching a person live and still get gradually worse and worse of a person is appealing and can work very well. Especially when the author is self aware and people love to see a horrible train wreck.
Once again your story not mines. However if your point is to make the audience go "aww cute" not "holy shit, this is horrible" then I say there is a flaw in your writing, cus that's not how it reads on paper.
Take it from someone who does write a lot of unhealthy relationships with (at least in one VN I did) end toxic couple best ending remaining together and tragedy ensues, with the point being its provides horror and intrigue in what can lead to this.
So don't ask is this to okay in fiction and more "What am I trying to do?"
Just provides the appropriate content warning to for people, please