That timeline and version of him was erased. In the end we see a new version of adult him living in a new peaceful timeline meeting his wife for the first time.Time re-aligns itself, then what? He just goes back to his awful timeline that he said is worse than Terminator, and lives in depression from seeing his wife alive and then killed a second time?
I guess it's just more about not seeing the protagonist actually get a satisfying ending to the story that left me pretty underwhelmed.
Final scene is him meeting his girl that you know is getting killed in a few years
The happy ending aspect is that inspite of the world changing due to time travel not being invented he still met the love of his life.