Real-life Sad Story

If I understand what you're asking ...

Well, I wouldn't feel bad about using that as a start-off point, mostly because I think it would change so much in the development and writing process, it would end up being someone and something completely different than what exactly happened.

But I would advise wholeheartedly against doing anything that makes you feel bad or uncomfortable. In that case, just go with your fictional alternative.

You're asking if you can use a real-life tragedy to inspire your fictional character, correct?

Yes. Yes, you can. Authors do it all the time. It's sometimes done as a tribute, sometimes done for closure, or simply because it provided inspiration. It's only morally questionable if you use your fiction to belittle that tragedy or make a mockery of it, IMHO. Just change the names and the details, but you can keep the basic structure.

If you're really conflicted, though, then ask the people involved. Or look around for other tragedies; read history books, biographies, or autobiographies. There's no shortage of tragic lives in the world.

Real life informs fiction all the time. Unless you have the permission and approval of all who were involved, it's probably a good idea to change the name and details of the situation to avoid hurt feelings, embarrassment, or defensiveness by those who may feel (rightly or wrongly) that their own actions are not being portrayed fairly or accurately. If this is to be a work of SF or F, then it sounds like whatever happened is going to be extrapolated into a completely different situation anyway.

Now whether a tragic story about a 17 year old who dies will fly is going to depend on your approach to storytelling. Not everyone likes sad stories, especially in speculative fiction. But some people are receptive to them. It will also depend on who the actual protagonist of the story is.

No idea where religion would come into it.

Where are we inspired, if not by life? I'd take it as an opportunity to tell his story.
I say go for it.
~Lev