I am that friend, and I have two other friends who do the same thing. There was a moment where my friend Joey and I didn't see each other for three years, and I got back in the area, called him, and we hung out for a week up in Boston. I bounce around, visit friends out of state or country a lot, or take jobs and projects that force me to travel or consume a lot of my time. So sometimes I won't see by best friends for months, even up to a year, and then we'll set up a day or two to get together and catch up and hang out.