Okay, I'll start with I have zero experience with any situation remotely like yours (except I was in college once, and I've had boyfriends).
But some thoughts occur to me. He lives with his parents, yes? I'm assuming they're paying for him to be in college? Probably best not to overly tick them off. Perhaps they pay his phone bill too?
I did lots of things to piss my parents off, but tried to not to them when I was living in their houses. (multiple parents)
It is wonderful that you've been open and honest and communicative. But do you do that because that's who you are, or because you expect it in return? I don't think deception will improve anything, if honesty hasn't.
Probably not much you could say to them, but perhaps time will soften them. And I don't mean a week. It's awfully hard for parents to let go of their dreams for their children. They're imagining they'll never get a wedding, or a daughter-in-law, or grandchildren. They're freaking out in advance over lost possibilities. I know that's a lot of why I had to continue pissing off my parents, to remind them that I was who I am and not who they dreamed I'd become. I'm not saying pissing them off is the answer; but I've lived through similar (after saying I didn't, how about that).
two cents, take anything that might be useful, forget the rest