He would have to renounce his marriage, renounce happiness, renounce everything.

Could he do such a thing after having pledged himself to her?
She had accepted him knowing him to be rich.
She would take him still if he were poor; but had he any right to demand such a sacrifice?
Would it not be better to keep this money in trust, to be restored to the poor at some future date.
And in his soul, where selfishness put on a guise of honesty, all these specious interests were struggling and contending.

His first scruples yielded to ingenious reasoning, then came to the top again, and again disappeared.
He sat down again, seeking some decisive motive, some all-sufficient pretext to solve his hesitancy and convince his natural rectitude.
Twenty times over had he asked himself this question: "Since I am this man's son, since I know and acknowledge it, is it not natural that I should also accept the inheritance ?" But even this argument could not suppress the "No" murmured by his inmost conscience.
Then came the thought: "Since I am not the son of the man I always believed to be my father, I can take nothing from him, neither during his lifetime nor after his death.

It would be neither dignified nor equitable.

It would be robbing my brother." This new view of the matter having relieved him and quieted his conscience, he went to the window again.
"Yes," he said to himself, "I must give up my share of the family inheritance.