So your boyfriend started at 5'11, 130, and has put on 20lbs in 2 years? what is his body fat %? If he REALLY is a hard gainer, 20lbs of solid, lean muscle and, I would assume, little to no body fat (I mean, the guy is 150... he cant be too fluffy!) isnt really that bad... He is too young and too small, I still agree with that, but it sounds like he has at least put some work in in the gym if he's gone from 130 to 150... thats a lot different than 180 to 200! That doesnt mean going on cycle is a good idea, but maybe at least his diet/routine may be better than we are giving him credit for. This is all allegedly second hand information, after all. Also... I know we cant discuss prices, but if we could, I would want to discuss how he only got THAT MUCH for $600... somebody didnt give him the homie price! haha
As to the aggression - if he is aggressive enough that you feel you should be worried BEYOND THE MEDIA BULLSHIT ABOUT THIS STUFF TURNING YOU INTO AN UNCONTROLLABLE KILLER (I mean, I think we have all slammed a door we normally wouldnt have, or picked an argument, or started a shouting match with our girl with little provocation while on cycle... but those are not dangerous side effects. Violence is, and some people do let the shit go their head!) then you are probably right. To call it roid rage puts too much of the blame on the steroids, when it is the user letting their hormones get the best of them (the same thing that pisses me off when one week a month my girl isnt quite as much fun to get along with

)... but the truth is that if you have a bad feeling about it because of HIS personality, you are probably right. I definitly reccomend he keep his cycle as simple as possible, and while there is nothing more simple than just NOT doing it, try to get him to keep it to test only, or like others have said AT LEAST drop the deca.
I dont know what more advice you want than has been given, but feel free to PM if you have a question that is unresolved that can be more succinctly worded, or isnt just "what should I do"... If I can help I always will, but at this point I am not sure exactly what the question is...