So I remember reading a story about a boy who ends up getting kidnapped and almost killed by Sombra on his way home from a reunion but when the teleport/portal fails(?) He ends up getting a piece of a cosmic heart. I though it was called 'One with the Heart' but it doesn't show up.

There are a few possibilities as to what could have happened:
1.) The title you wrote is incorrect.
2.) The title has been changed by the author.
3.) The story was deleted by the author.
4.) The author deleted their account on FimFiction.

I remember this one as well. A typical Isekai power trip fantasy. The mom was the previous weilder of the heart. Near godlike abilities, his world gets wiped out and all he manages to save is his sister. That one right?
I never did catch up to the most recent chapter when it could keep my interest.
I looked as well and it was nowhere to be found. You might at least find the author and title using the wayback machine, though I don't think it saves the stories.
(Also try enabling mature mode? Sometimes the ratings shift.)

It got deleted, but you can still read it here: https://fimfetch.net/story/230723/the-one-with-the-heart

Oh what, I didn’t even know it got deleted!? That’s a shame, too bad bad not many people would ever know of it’s existence. But thankfully, it’s still preserved in Fimfetch!

7695211
Thx’s for the link, really appreciate it!

Did Spooky Ghost delete his profile?

Also seems like some of the story is missing from fimfetch QQ sad panda is me