The building I lived in had a rooftop pool, an elevator and a workout room one floor above my unit -- lavish features for college kids.

But I never imagined that this beautiful apartment would cost me a friendship.

For my first three years at Northwestern University near Chicago, I lived in a dorm and then a sorority house. Each year, my dad paid for housing costs and meals. I never had to negotiate bills with my roommates or find sublessees for the summer.

That changed during my senior year, when I leased a two-bedroom apartment with two of my best friends -- and paid my share with my own money.

The city of Evanston's housing market is not cheap. Sure, some students find houses far from campus with rooms for $500. But less than a block from my classes, my apartment cost more than $2,100 a month. My share: $640.

It quickly became difficult for me to split expenses with my best friends. Even though we'd shared secrets and inside jokes, I was constantly embarrassed to talk about money with them.

Finances are a huge source of tension among friends and couples, and people often try to avoid these conversations, said Margaret Shapiro, an assistant director of the Council for Relationships in Philadelphia. For many people, money evokes emotions of dependency or independence.

"It just brings out so many feelings and fears and yearnings and differences among friends, as well as couples, that aren't acknowledged, " she said.

In my case, I knew money would be tight my senior year. My dad is widowed, and my sister starts college next fall. So I saved every paycheck from my summer internship, and I drove a campus safety car a few nights a week. This money paid for all of my senior-year expenses -- my meals, apartment, books and more.

My roommates, whose parents paid for their rent, knew about my tight budget, but we decided to live together anyway.

From the beginning, apartment costs caused tension that I didn't know how to ease.

At first, four of us chose a three-bedroom apartment, but one friend bowed out before signing the lease. My roommates wanted to stay and pay about $1,000 a month in rent. I said we needed to downsize to a smaller, cheaper place. We did.

Additional costs created more squabbles. Which roommate would buy the vacuum, the IKEA dining table and the pots and pans? How would we split the rent, especially since I shared the master bedroom? And who would rent my share of the space when I left for the summer?

The biggest price tag, emotionally and financially, came at the end of my time in the apartment. As I prepared to move to South Florida for my internship at The Miami Herald, I searched for a sublessee -- with little luck. My roommates were stressed, too. They didn't want to readjust to a new person in their space.

During a terse talk at our dining table weeks later, my friend with whom I shared the master bedroom said she would not allow a sublessee into the apartment. My roommates offered to pay half of my rent if I kept the space open, but we negotiated to two-thirds.

The conversation ended with tears and silent stares. My other roommate, who had her own bedroom, said this was just a business transaction that didn't affect our friendship. She still calls me on the phone.

But this experience taught me that I can't separate my friendships from my money relationships. I wish someone had warned me about what I later learned -- living in dorms and on-campus houses keeps money talks from infiltrating college friendships. But as soon as lease agreements are signed and monthly bills pour in, the dynamics change. Some people spend money freely; others scrimp and save. You don't know which category your friends are in until you live with them.