Please answer a question about the following article about Dominican Order:

Dominic's search for a close relationship with God was determined and unceasing. He rarely spoke, so little of his interior life is known. What is known about it comes from accounts written by people near to him. St. Cecilia remembered him as cheerful, charitable and full of unceasing vigor. From a number of accounts, singing was apparently one of Dominic's great delights. Dominic practiced self-scourging and would mortify himself as he prayed alone in the chapel at night for 'poor sinners.' He owned a single habit, refused to carry money, and would allow no one to serve him.

What did Dominic greatly struggle with?
relationship with God