"In 2000, when the BJP had 67 legislators and the JD-U had only 34, we said that the JD-U is our younger brother... Bihar's chief minister should be from the JD-U. We accepted Nitish Kumar as chief minister," Singh said.
"Why did the JD-U snap ties (with the BJP)? What was our mistake? They have disintegrated our emotional relationship of 17 years," he said.
Singh also defended Gujarat chief minister Narendra Modi and the BJP's decision to appoint him as the head of the party's campaign committee for the 2014 general elections.
"To be successful in the general elections, we have made Narendra Modi the chief of the election campaign committee. Is that my mistake? Every political party creates a campaign committee for any elections. Was the JD-U angered just by this and snapped such old ties?" he said.
"If we made Narendra bhai (Modi) the head of the campaign committee, did we make a communal person the head? If an unfortunate riot occurred in Gujarat in 2002, should the chief minister be held responsible for it? Such riots also took place under Congress governments, but no one calls them communal," he added.
JD-U president Sharad Yadav announced on Sunday that his party had ended its alliance with the BJP. He also quit as convenor of the BJP-led National Democratic Alliance (NDA).
The JD-U had been upset over Modi being made the head of the BJP's poll campaign committee over allegations of Modi's "approval" to the 2002 communal riots in Gujarat.