Can i get a disease from a blow job?

Yes: It's a very efficient way of transmitting gonorrhea to the throat. You can probably catch infectious mononucleosis and/or cytomegalovirus this way. Whether HIV can be transmitted efficiently this way is controversial -- three classic large studies had negative results but think about a condom in any case.

Of course. There is no scenario in which any STI/STD you could get from unprotected vaginal or anal intercourse could not also be transmitted vial unprotected oral sex. Best answer is a condom.