The song "So Long" by Niall Horan (featuring RTÉ Concert Orchestra) explores the themes of missed opportunities and the realization of love after a significant amount of time has passed. The lyrics reflect on a relationship that should have happened sooner, but despite the delay, the love shared between the two individuals is strong and genuine.

In the verse, Niall Horan expresses his recognition that their relationship had been unconventional and filled with obstacles. However, he also acknowledges his faith in the connection they still share, as both parties had always kept a special place in their hearts for one another.

The chorus poses a question, wondering why it took so long for them to acknowledge their feelings and commit to the relationship. Niall Horan emphasizes that the love they share has been apparent since they were young, possibly alluding to a long-term friendship or a history of missed chances.

In the second verse, the focus shifts to moving forward and making up for lost time. Niall Horan mentions his determination to not let the opportunity slip away this time, as he firmly believes that the other person is meant to be his.

The bridge suggests a sense of disbelief and astonishment, as Niall Horan expresses that they have just begun to realize the depth of their connection. There is a recognition that they no longer have anything to prove, now that they have come together.

The outro repeats the question from the chorus, indicating some lingering confusion or frustration about why it took them so long to embrace their love fully.

Overall, "So Long" conveys a bittersweet sentiment, exploring the delayed realization of love and the longing to make up for lost time. It emphasizes the idea that love can withstand the test of time and remain strong, even after missed opportunities and long waits.