I recently read an EW article that gave us Mark Hamill’s own version of what happened to Luke before The Force Awakens.

http://ew.com/movies/2017/12/04/star-wars-mark-hamill-luke-skywalker-backstory/

According to Hamill, Luke Married a widow with a child, and withdrew from the force to raise the child. Apparently, the child dies tragically because it gets hold of his lighsaber and kills itself.

To my mind, this is a satisfying backstory. Luke gets a happily ever after moment, but (as usually happens to Luke,) there is a tragedy beyond his control. This could probably be hinted at in the TFA forceback scene.