So you got offended because from your perspective, your roommate suggested that the course of study your girlfriend has taken is easier than the one he took. Seems like a pretty valid assertion, if we're talking about academic rigor...some disciplines simply require more time and effort than others. That is a fact. So why'd you get offended? You fell into the trap that pretty much every student falls into. The trap that says, if you are not smart and you don't work your ass off, you aren't worth anything. Self worth is not determined by what you study, how much you study, your raw intelligence, and sure as hell isn't determined by a GPA. You're confusing completely separate aspects of life. Just because someone is studying something that isn't as challenging as engineering, doesn't mean that what they're studying isn't important. Furthermore on a societal level, it sure as fuck doesn't mean that we don't need those people (in elementary school teaching, social work, etc) to do what they do and do it well. Raw intelligence doesn't translate directly into your value to society. I'm adequately intelligent, but I'd be a piss poor elementary school teacher.

So back to the original respect thing. Did your roommate insult you or your girlfriend? No. He said the study wasn't as rigorous. He's correct. But that says nothing about your value as a human being. That was a connection you added after the fact. You need to learn to separate those two things, which is exceedingly hard for most (me included) students to accept.