Updated

Retired Rep. Mark Souder says he doesn't know what motivated him to commit adultery with a staff aide, a decision that forced him to pack his bags and leave Washington last week.

"I don't know. Obviously if I knew the answer to that question, I wouldn't have done it," Souder, R-Ind., told the Fort Wayne Journal Gazette.

In the interview published Sunday with his hometown newspaper, Souder said that Tracy Jackson had been more than just a love interest; she was a close adviser who lived in Syracuse but had an acumen for northeast Indiana politics.

"Tracy held her own with some of the smartest staff people in Washington," he told the newspaper. "Our relationship developed because of this, not the other way around, as some have implied."

The former congressman said he planned to bail out of his re-election race this year even if he hadn't been caught in the affair with Jackson, an adviser who conducted mock news interviews with Souder for Christian radio broadcasts.

The eight-term congressman won a hard-fought primary just weeks ago. He told the newspaper he decided he wanted to withdraw to let new Republican blood enter the race in the conservative district.

Yet Souder said he also debated wading through the ethics probe that was to follow news of his affair, if only because no one had proof he and Jackson were intimately involved. He said he changed his mind when his advisers laid out for him the expense of a House ethics committee inquiry and the impact on others around him.

He said the relationship ended after the couple was spotted in a car at a wilderness preserve. A lot of what-ifs then went through his head.

"Why would somebody who's almost 60 years old and been a congressman 16 years do something juvenile?" he asked himself. "Subconsciously, was I wanting to get caught? Or was God so frustrated with me he said, 'I’ve had it. You're so stupid here I'm going to, in effect, out you.'"

With the relationship now six months over, Souder said he will only talk about the gritty details in marriage counseling with his wife Diane.

Click here to read more from Souder discussing his affair and career implosion.