Originally posted by jaden_2.0
The prevailing theory is that he was always married to her in the main timeline and because she was an awesome spy she managed to keep it a secret and that's why the ending can be the same timeline and his staying in the past and not returning via the machine doesn't mess things up.
That’s not accurate and it wouldn’t make sense anyways, as that would still involve the past changing. Just keeping it a secret wouldn’t stop it from becoming an alternate reality, lol.
I just explained it up too, if you wanna get a decent idea of what actually happened, and why.