Ok so im 17 and im emancipated from my parents, is it illegal for me and my bf to have sex, hes 21?

Answer 1

Possibly not, but it would have been so much more helpful if you had stated your location. It is your age where any problem would lie. Assuming that you are in the USA, then it depends on the state - there are some states where you have to be 18. Take a look at this list, and the wikipedia map, and just be grateful you don't live in one of those countries where any sex outside of marriage is illegal.
http://www.avert.org/aofconsent.htm
http://upload.wikimedia.org/wikipedia/commons/e/ef/Age_of_Consent.png