Bruce imprisoned himself in the cave. Restraints that allowed him to walk all around but never leave..

He didn't tell a soul about it wanting to stay there for the rest of his life. Isolated viewing himself as a time bomb. The loneliness was outweighed by his fear.  He didn't bother to take care of himself properly.  Survival under minimum conditions despite the supplies he had in abundance.

He planned on dying alone, and for no one to find his body.. Thinking he was sparing everyone...

At first it was weeks since you heard from Bruce... Then those weeks turned to two and a half months...  Your searched for him you found him.... He didn't look you in the eye just staring at the rocks.  Thinking out loud from madness, speaking his mind or trying to convince you to let him suffer.

"I got a poison in me.... spreads, it can infect even the healthiest people....I removed the poison.... I fixed it..."