Looks like Alex and Maggie are super happy on Season 3 (so far). The following is from blastingnews.com:

Alex and Maggie could possibly be engaged or married in the upcoming season 3 of “Supergirl.” New reports are circulating some cheesy moments of the two characters. In a clip posted by Twitter user Manuela Lima, a behind-the-scene clip seems to have been leaked. In the tweet, the couple can be seen filming an intimate scene for the new season. The less-than-ten-second video shows Alex and Maggie will lock lips. Meanwhile, more spoilers floated on the web that seems to confirm the level-up relationship of the couple. Hollywood North Buzz posted several behind-the-scenes photos of the couple. It appears that the two are having a nice conversation while taking a walk in a garden. However, one aspect in the photos will capture the eyes of the fans of “Sanvers.” In the image, the two characters seem to be wearing something that sweet couples do. Alex and Maggie are both wearing a ring on their left ring fingers. To make it more interesting, the rings they have are matching! With the kissing scene and the matching rings, one could not help but speculate that the two characters have levelled up their relationship in the upcoming season 3.