Student or Learner
He was in a terrible state. It was probably the pressure that tipped him over the line.
--- "tip over the line" - what does it mean?
He may have been having difficulty making an important decision, such as, "Will I pick up that gun and go and rob the bank or not." The pressure of possibly thinking about his terrible financial situation, and all that money in the bank tipped him over the line of whether he could still think rationally or not.
I am not a teacher.
I would go with searching's explanation here. 'Tipped him over the line' sounds to me like he was pushed into doing something that normally for him was unthinkable. 'Tipped him over the edge' would suggest that he was pushed into madness or a mental breakdown.
The word "line" is used in other situations.
"There is a fine line between genius and madness"
"The line has been drawn in the sand." This can be in a military or confrontational sense. One party is of one opinion, the other the opposite.
"Don't cross or I will not cross over that line." Meaning that someone has taken a stand, and will not budge.