If you are post college and move to another city, naturally people at work you connect well with will eventually become friends. I am kind of an introvert too and since i spend most of my freetime with my girlfriend it is hard to meet new people outside of work and spend so much time with them so they become real friends. But isn't it the same as in college or school ? Most of your friends are people you spend considerable time with and that is often work/school/studying.