Oxford University researchers asked people about their inner core of friendships and how this number changed when romance entered the equation.
They found the core, which numbers about five people, dropped by two as a new lover came to dominate daily life.
"People who are in romantic relationships - instead of having the typical five [individuals] on average, they only have four in that circle," explained Robin Dunbar, a professor of evolutionary anthropology at Oxford.
"And bearing in mind that one of those is the new person that's come into your life, it means you've had to give up two others."
via bbc.co.uk
If getting in a new relationship will do that, I shudder to think what starting a startup will do. =)