I forgot to discuss...:P...hmm..of course there's the sniffing...that goes without saying...Brian and Justin seem to have a sense of smell in regards to each other that is quite powerful...I don't have and icon for it but obviously the famous "smackling" scene when Justin returns home from shopping with Jennifer and sniffs Brian all over....
mainly for me, it's love....I think the nuzzling is something they do with each other that neither would do with anyone else...it's about closeness and affection and touch...beyond something purely about sex....it's connection....