When astronauts go outside of the International Space Station to conduct spacewalks, they have to wear special spacesuits in order to protect their bodies from the harsh space environment. Not only would the vacuum make it impossible to breathe and the lack of a protective layer would expose you to radiation.
Because space is a vacuum, the oxygen in your body would depressurize and expand to twice its normal size, which means your body would expand as well. You would quickly experience asphyxiation from the lack of oxygen and inability to breathe, and your body would eventually freeze solid from the cold space around you.
After you die, which would take just over a minute, your body would float around in space in its current form, potentially unchanged and frozen solid, for potentially millions of years. Gut bacteria would be eating you alive from the inside out throughout this process until they themselves eventually succumbed to the vacuum of space.
While it would be impossible for a human to live in the vacuum of space, spacesuits enable the body to remain in a pressurized state and at the proper temperature without boiling or freezing. Unfortunately, spacesuits are quite expensive and we're running out of them, so NASA will have to come up with a new design soon, otherwise we'll be dropping out of spacewalks in the future.
