How and when does Darren develop an attraction to Connor?

In the scene where Darren is consoling his brother, he seems genuinely shocked at the kiss on the cheek. There was nobody else there so I don't think he was just pretending he didn't like it. It definitely came as a surprise. So are we to assume he was hiding feelings for his brother at this stage, which only manifested later on when he found Connor was attracted to him?

Darren saved Connor's life, but it would be ridiculous to cite that as a main reason. Of course it would be complex, but it'd be interesting if the film at least addressed why/how and when, over what kind of time period, this incentuous relationhip developed.