The conversation went as is.

Neptune: "I don't know man, it feels like you're just letting her go."

Sun: "It was never about that, braniac!"



It's not Sun saying that he was never in love with or interested in Blake, it's him saying that her happiness and safety is what was most important to him. That his feelings for her weren’t the only/main reason he followed and risked his life for her. If anything, I think this just makes his feelings much more genuine than before, because it shows that Sun (unlike Neptune who's had a much more womanizing/flirtatious approach with women) is more than willing to put Blake's needs over his own and Sun is also willing to wait for Blake to overcome her pain and issues with her team first.