Its a story of a boy whose friend dies in an accident. He runs too a tree stump or fence and travels through a portal and ends up in a reality where he died instead and his friend lived. However this life there is different because it seems as though MC died when he was younger. Oddly enough his sister exists and is the same age. No dad.

So his best friend is friends with this nerdy kid who watches this movie about ants and how the ending is different in the two worlds.

There's also something about a guy who follows the MC through the other world and learns that the him of this world has a family whereas back in his world he's alone because his adopted old man died.

MC has a sister and mom. AU Mom thinks that MC is playing a prank pretending to be her dead kid.
The kid matures over the course of the next few chapters as a result of talking to his mom, the guy who follows him through the portal and the nerdy kid. He becomes more aware of danger in the world.

Manga ends with him choosing which of the two worlds to live in. I think it had 12 chapters total but there may have been a 13 or 13.5/14 for a special author note thing.

I've been looking for 2 days now and nothing. Please help.
😢 😢

I thing it's Inai Boku wa Hotarumachi ni Iru.

You're everything, you're everything I'm notI'm anything, I'm anyone you want

Thanks so much! When I was looking for it I overlooked this cause I had assumed the title started with a H and the cover was different from what I remember! 😀