Another time travel conundrum...
I'm going to simplify this as much as possible.
If David goes back in time to correct an event--to kiss Jessie--thereby causing him to hook up with Jessie.
Now the very reason he went back in time no longer exists.
Shouldn't he cease to exist the moment he kisses Jessie since the reason he went back no longer exists therefore he never would have gone back to that point?