Business is called business for a reason. It's hardly ever fair. Finally, if you don't pay attention, it can take you out at the knees before you even know it. If you really want a friend, buy a dog because you aren't going to find many true friends in the working world.
Now don't mistake this as a rant against friendship. On the contrary, I think you better have friends in life or you're really in for a rough ride. Unfortunately, I see too many people seeking friends in the business world and oftentimes mistaking business partners (or acquaintances) for friends. If you thereafter expect them to behave like friends, the shock and betrayment when they don't stings even more.
As of late, I realize this increasingly when it comes to people just entering the workforce. Life and work have become so intertwined that it's difficult to keep the two apart. Don't get me wrong....you can find friends in the working world and many times, you'll have no choice. This is fine as long as you understand that there are different dynamics at play when it comes to work verses a university environment for example. Competition and "getting ahead" change when it's about money. Go ahead, be nice and learn to play "the game" of business which will regularly involve "social" events. Yet remember, these are "acquaintances" and not always friends. They may be using you to further their career or chances. You may simply be a pawn in their strategy. At the other end of the spectrum, you could just be a distraction. As long as you're aware of it, not a big deal.
You will learn to balance things out and judge for yourself who is friend or foe. This unfortunately remains one of those things you'll learn only with experience. I've yet to find the book on this. Until then though, stay alert and go take the pooch for a walk!