He could just be processing. Or he could be scared. Of he could be in trouble with his gf.
I've had open and honest and fast paced discussions cut off by other events (in your case the friend's house). It can be really hard to figure out how to start them back up. It can be even harder if you got information back you were not expecting. For instance, the love doesn't HAVE to be unrequieted after all. He may have been expecting "thank you and I feel the same but we're both in happy relationships". It would have allowed him to get his feelings out there and be known, but still have that "safe" zone of knowing nothing could ever happen. And then you blew him away with a whole new possibility.
Let him process if that's what he needs. An let us know if he does get back to you. And, if this doesn't work, at least take away from it the closeness it has brought to you and your husband and that first thrill of being able to openly tell a love interest of your interest and relationship status. I'm sure it was freeing.
I'd rather be hated for who I am than loved for who I am not.