There's no reason he can't be your pal on FB. That's just silly.
As for the rest of it, I'm sorry about how things are. But how much does his family know? Is it, "We hope you meet some nice girl soon and settle down, here are the names of 3 possible choices?". Or is it, "So nice to see you again, AZAndy, our son's 'special friend'."
True story-- when I was in high school in the late 70s, a friend had a lesbian older sister. And their conservative parents referred to Mary as Michelle's 'special friend'. It wasn't disrespectful so far as I could tell, and I know Michelle wasn't bothered by it. It was more that their parents most likely knew the score but couldn't bring themselves to say it out loud.
Imperfect? Yes. But it never seemed as if it was done with malice.
Finally, your husband really should be open with his classmates of all people. "Oh, you like that car? Thanks, it's my husband's."
I hope he can eventually feel comfortable enough to say as much.