Overall it's a fine and dramatically sad short story but it left me with a bad impression near the end as MC sees an alternate future if his mum didn't have him with her soooo much happier in it.
He questions if he shouldn't have even been born and existed which would get some readers with similar circumstances as him to question their lifestyle in a such negative light. Especially because there's no resolution if the mum is truly happier without him or not, with the answer being "it is better, at least I have [love interest]". So some readers may end up having extreme thoughts about themselves with no closure leading down a spiral of negativity, those kinds of stories should not be glossed over but spend more time on introduced themes.
If it wasn't for the weird uncontrollable time travel stuff it would have been a really nice short manga but it became too complicated with weird messaging, it should have just stayed a simple romance with a bad ex.