You should find something to do in your life. An aim. Perhaps join a club to make new friends or pick up a new hobby to take your mind off your previous aquaintainces. Read a book? There are many things you can do! Pick up a new language, volunteer in some charity organisation... something meaningful. what's your interest? Since you are free enough to "stalk" people, why not use the time for something else? you wont think of such demoralising things when you occupy yourself with other things. When you start working you wont have as much time for yourself. Make full use of your free time.
Being quiet and shy is not necessary a bad thing. Imagine if all the people in the world were social animals.

Think of your good points! Your friends may not have the good points that you have...
Anyway, i dont think checking out other people on friendster is called stalking behavior. It's more like kaypohing around. I bet a lot of ppl does that.