I dont know why this makes me so upset?

whenever my roomate has a guy come over, i get severly angry. i get irritable, and upset to the point where i get an upset stomach. i have a boyfriend, (he is in the army and lives several states away) but whenever she has a guy come over it makes me so angry i cant stand it. i imagine its jealousy because my boyfriend isnt right here to 'hook up' with all the time. it gets aggrivates me SO bad and i need to be able to get over it. why would this be bugging me to this bad of an extent? she has someone over right now and i cant even concentrate enough to study for this test because im so angry that hes even here. it also makes me mad because her bed is right up against a wall that is my bedroom wall and i can hear them knocking into it. this seriously drives me insane. other people would be giggly and asking questions and excited for their roomate. not me, i just want to get out. i really need some help here. i cant deal with this feeling.