Aaron White, co-founder and CTO at open textbook startup Boundless, will be ending his day-to-day role at the company at the end of this week, BostInno has learned. White will remain on the board and will serve as an adviser to the company.

A source tells me the decision was a mutual one between White and co-founder/CEO Ariel Diaz.

White told me his move is based on the belief that his skill set is best suited for very early stage companies. “It’s bittersweet because this is my home and this is my family. But it’s ultimately the right thing for the company and for me too,” he told me.

As the company’s technical co-founder, White played a wide ranging role in product, engineering, marketing, and strategy since its founding in 2011. However, as the Boundless management team has expanded, White has seen his role shift. Matt Hodgson, formerly of TurningArt, was hired as VP of Engineering a year ago, and has been running the engineering team since then.

As a company grows, the boundaries around roles in engineering, product, and management firm up, and that process appears to have prompted White to reconsider his particular skills and interest. “It’s important to realize where do you fit,” he said. “That’s something I’ve thought about for a long time.”

Diaz said the board and management team have been supportive of White’s decision and are excited to see him staying on as a board member.

Both Diaz and White were quick to point out all that Boundless has accomplished and the momentum it has had lately. The company recently announced that 500,000 users have accessed its textbooks. “As a company, we’re firing on all cylinders,” Diaz said.

White said he’s not yet sure what he’ll do next, and is considering traveling as well as new projects. “This decision isn’t being motivated by some burning call to go do something else.”

Boundless’ third co-founder and CMO, Brian Balfour, left the company in September of 2012 and remains an adviser. Boundless has raised $9.7 million in funding.

UPDATE: Aaron offers his thoughts on his transition on his blog.