West Midlands MEP Bill Etheridge quit as the party's sport spokesman in protest at Mr Bolton's refusal to stand down and urged party members to oust the leader.
Mr Bolton deserted his wife and their two young children at Christmas after meeting Jo Marney, a model and Ukip member who is nearly 30 years his junior.
A Sunday newspaper printed texts it said had been sent by Ms Marney about Prince Harry's fiancée, including use of the word "negro" and a message reading "This is Britain, not Africa", during a discussion about the royal engagement.
But his future as Ukip leader now hangs in the balance while his marriage to Mrs Smurova-Bolton is also over.
The U.K. Independence Party has suspended the membership of the girlfriend of the party's leader after she made racist remarks about Prince Harry's fiancee, American actress Meghan Markle. "And a black King", she was reported to have written.
In a statement, Ms Marney said her remarks were deliberately exaggerated to make a point and were taken out of context, but "I fully recognise the offence they have caused".More news: American Electric Power (AEP) Earns Coverage Optimism Rating of 0.11
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The Ukip leader said: "The romantic element is over, I'm afraid".
The party has struggled to find a role since the Brexit referendum and has been beset by infighting.
Alluding to ethnic minorities in general, Ms Marney writes that "they are pushing their way to the top slowly slowly. And a black king", the Mail said.
Markle, who will Wednesday Harry in May, has spoken publicly and written about being biracial, including how it affected her acting career.
Ms Marney, who apologised on Sunday for her comments, has already been suspended from Ukip.