Whenever you make a decision, the option you did not choose spins off a parallel universe. The more options there are the more parallel universes will be created. Now you might be wondering what that has to do with time travel and coming back home from the past. Since there are uncounted decisions being made across the universe every nanosecond, are you sure the home you came back to is the right one? How many parallel universes have been created since you left? How may of those parallel universes will never see you again, but will hold out hope that you will come to what they consider home?
When a person travels back in time, every decision made in the universe will have to be taken into account. You might not think that an being on another planet could affect your timeline, but that alien could be making a decision that ripples across the vastness of space and affect your home base, even if that decision is how to take the alien civilization’s version of coffee.
Another thing to consider is the variables that go into when you leave. If you have a window of one minute with 60,000,000,000 nanoseconds in it, it is possible that you have spun off 60,000,000,000 parallel versions of yourself. It is possible that you could run into one of those parallel versions of yourself while trying to get back to the home.
So, how hard do you think it would be to create a system that will correctly navigate you home from the past? How many parallel versions of your lover are you willing to leave alone to travel into the past?