Poor John has like 4 different versions of reality
Must be tough on him lol.
"It looks a bit sweaty in there so you may need to apply baby powder" Zapp Brannigan
Yeah, you actually do have to watch the movie a couple times through to understand how reality changes for him and his personality changes as a result. They don't just announce right out, "OK now history has changed" -- you have to figure out when it happens each time.
At first it seems to be bad writing; his character seems to act inconsistently. But when you think about it, the traumatic events in his life are all switched around -- first his father dies when he was 6 years old, then his father survives until 1988 but it was his mother who is murdered in 1969 -- both those events make him unable to enter a healthy adult relationship.
It's only at the end, when Frank is able to prevent Julia's murder and also quits smoking in 1969, allowing them both to survive to 1999 and beyond (when Frank finally ends the cycle by blowing away Shepard) that John becomes a healthy adult, and he was able to have the family he should have had all along.