Is “Ugly Betty” the first tv program to show two gay young men (Justin and Adrian) kissing?
Prior Art:
This Life (1996-97)
Queer As Folk (1999-2000)
Not sure if these ever aired in the USA though, if that was the scope of your question.
Ah, I meant to specify: prime-time big three USA networks (CBS, NBC, ABC) and not premium channels (HBO, SHOWTIME, etc.) Thanks, though.
Depending on whether you count shows on the WB, there was the kiss between Jack and Ethan in the third season of Dawson’s Creek. Perhaps still significant is that Justin and Austin (not Adrian) where portrayed by actual teenagers, whereas the actors on the Creek were well into their 20s.