my thoughts on time travel are that, in situations like this, it is a complete
truth and stuck in an infinite cycle.
SO, future simon came back in time because when he was at this point in time, there was a future simon that came back and told HIS alisha how to do thngs, so that our current future simon, back when he was nerd simon, would become the man he currently is.
In the exact same way, our current nerd simon will turn into who he will in the future, but he knows that for that to occur, he must, in the future, come back in time and tell alisha whatever and do whatever so that things happen in a certain way, so that he becomes who he becomes.
you're sitting in your chair. suddenly a portal opens and you from 5 years from now walks out and says "here is a ray-gun. use it to take over the world." you then use the ray gun to take over the world, create a super-think-tank, and develop a time-machine. you then use that time machine to go back in time and give yourself the ray-gun (which is now a standard-issue gun, in the future) because if you dont go back in time, you would have never been able to take over the world, and the future as you know it (which would be the present, in the you-from-5-years-from-now view) would simply cease to exist.
so because you dont want the future/present to stop existing, you must go back and enable yourself to become what you currently are.
the harry potter fanfic that is like 800 pages long investiges the timetravel 'paradox' quite interestingly. harry recognizes that when hes sitting in his chair, he can simply wish for an item to be, say, behind a door that leads to the hallway, and then go and open the door and the item is there. he then uses the item to escape the situation he is in, get back to the dorms, and uses his time machine to go and place the item behind the door, back in the past at the time when he needs it. it is near god-like powers, because all he needs to do is have the intention/wish for something to happen (that is within his power to cause to happen further down the timeline) and it will happen immediately. and really, i dont see any problems with this, and it is even a stretch further than the simon time traveling.
SOOOOO in summary, future simon is who he is because there was another future simon who made him that way, and THAT future simon was made that way by HIS OWN future simon, continue in an infinite series. similarly our current simon will have to eventually go back in time and do the exact same thing that future simon we have seen done. his fate is locked in, essentially. if he chose not to go back in time, i think that the instant that decision was made in his brain, the world would .. i dont know the word... warp? itself and create a completely different image based on what would have happened if no future simon had come back in time. and simon would instantly forget having thought of going back in time, because it never happened to him.
so if we only have one reality//linear timeline, it is a reality in which simon either HAS, or HAS NOT gone back in time to to whatever hes done. since we have established that he has, we see that logically, he too must go back in time, or else future simon would have never gone back in time in the first place.
..... anyone follow all of that?

:lol