Okay, this is assuming that JGL’s character in Looper comes from the future and settles in the present. (Or maybe he just gets his hands on a time machine. IDK)
So Joseph Simmons (JGL’s character) is [accidentally] sent back in time to the 1930’s where he meets the Bondurant’s - specifically Forrest. Stuff happens and they fall in love.
Do with it what you will, whether Joseph is pulled back to the future or stays in the past, it’s all up to you.
This has been in my mind for god knows how long and I don’t trust myself not to butcher this.