Serious read the book i recomended, it goes through all the emotions you're displaying above.
You CAN have 2 families. Your adopted family and your biological family. You adopted family will of been the one you grew up with anyway, you should explain to them that if you do go looking for you biological family, they will never replace the family who brought you up.
Obviously you want to know where you're from, everyone does. You want to know if you look like your mum or you dad, what if the history of your biological family etc.
Its definatly natural to want to know more, in a way by finding out about your biological family your finding out alittle bit more about yourself.
Maybe wait till you're 18 (if you're not already), and start looking more intensivly, it will be an emotionally hard time for you and you're adobtive family, but if its something you feel the need to do, go for it. Your family adopted you, and i'm sure they expected you to go through this once you grew up, and you have.
Once again good luck what ever you do.
Oh and i'm no expert on adoption, i just found the book i read last night really touching, you sure seriously read it.
Oh and i'm eastern european too!