For the people start a startup then it has to be worth it, because you're putting everything on the line. To him the relationship obviously wasn't as important as the startup's success. And if it got in the way? It had to go. With startups, there are only binary outcomes: wild success or abysmal failure. If you're betting everything on wild success, then sometimes you have to make those choices.
(I'm using startup in the sense of "high-growth new business")