Apparently happened several months ago (March / April.) Chyler Leigh (Alex in the SG show) has tweeted identifying Blake as Melissa's "hubby". If you check out the comments section
you'll see various Supergirl fans (inc. myself) discussing this Monday, as the news started to break post-Comic-Con. It was Kelly (of the superherohype.com forum fame) who spotted the wedding ring and figured out this had happened some months back, and then I posted Chyler's tweet.
(Very) belated congratulations to Melissa, Blake, and their families. I wish the happy couple all be luck in the world, and hope they'll have a great life together. Wonderful news.