That's what many people do.
You're learning to say no, that's a good thing. There are many
people out there who just wants to make use of us. Don't let them
do that.
However, for those people who really needs your help, or
appreciates it, these are friends worth keeping, for you may need
them to help you in the future.
And i do believe that being nice comes in a circle. You be nice to
people, people will be nice to you.
But sometimes we get the jerks and idiots, and that's when we stop
being nice to them.
Good luck on the beginning of your new life~