John Cena -- Why His Marriage Fell Apart

It's becoming apparent why John Cena's marriage to his high school sweetheart fell apart -- the house they were remodeling was sending them to the poor house and the courthouse.

We've already told you -- Cena has blamed the divorce on the remodel, claiming it caused unbearable strife between him and his wife.

We just found documents showing how bad the situation was ... one of the contractors filed a lien on the house for $110,000, claiming the Cena's didn't pay him for his work.