There are too many heart eye, lady-loving lesbian, I-wanna-have-your-baby, moments between Kara and Lena for their relationship to be purely platonic.
The writers and producers and directors must realize the moments between them that imply more and clearly like those moments because they occur quite frequently.
And they didn’t have to cast Katie McGrath, a woman who often plays lady-loving roles as Lena, but they did and it seems like too much of a coincidence to not be important.
And lastly, the actresses have so much chemistry that it would be a crime if the show didn’t take advantage of it in some way other than friendship.
Although, I don’t think that they will ever put Kara and Lena together. It breaks my little gay heart and enrages me all at the same time.