Even though we were becoming closer and closer, we remained just as friends.
Although we were becoming closer and closer, we remained just as friends.
Which is the one above correct?
"Although" is a way to show a contrast between what you say and what it is.
"Even though" is preferred when you say something that bring to a negative concept, but the result is positive. "example: Even though Einstein took an F in math, he won the Nobel price"
So, in this case, I think that is better with "although".