this guy stares at me constantly, especially when I'm with guys. He checks me out and he comments on everything I say. When he sits, his legs are open and sometimes he violates my personal space etc... Does this mean he likes me?

It could be that, but my first impression is that he's a creep. Although some guys don't know how to express their feelings for someone and resolve in being creepy. That's why, it really depends on the person. Maybe, just once or twice, try talking to him. See his actions and behavior while he's talking to you. That should give you a bigger picture on what his intentions are actually.