Apart from the parallels with Kili and Tauriel, I think the hugest and most obvious hint at Thorin and Bilbo being in love with each other, was Bilbo being unable to say that Thorin was his friend to Balin. AND IT’S SO IMPORTANT that it was Balin that he couldn’t say it to. Because Balin knew. Pay attention to his expression when Bilbo is trying so hard to say what Thorin was to him. It’s an "I know, you don’t have to say it", look and you cannot tell me otherwise. I believe that Bilbo wanted to say that Thorin was his friend because he’s already lost a friend. If he admits out loud that he was in love with Thorin, it’ll be like losing him all over again, but as so much more. So he wants to tell Balin that he was his friend, but the look on Balin’s face let’s him know that he knows better. So he says nothing. It’s only months and months later, in front of a group of hobbit who wouldn’t know any better, that Bilbo finally says that Thorin was his friend. He still hesitates, because he’s still not sure if he wants to admit otherwise, but in the end, he can’t bring himself to.