This is not a love song. It is a claim of ownership disguised as regret. Bieber admits to mistakes but never says what he did, then demands she accept his version of reality where her moving on is wrong and his suffering proves he deserves another chance. The repetition of 'that should be me' is not mourning, it is insistence that he owns a role someone else now occupies.
Did you forget all the plans that you made with me? / 'Cause, baby, I didn't
He frames her moving on as forgetting, like she is suffering from amnesia rather than making a choice. His memory becomes evidence she is wrong, not that he still cares.
You said you needed a little time for my mistakes / It's funny how you used that time to have me replaced
He admits fault but treats her healing period as a betrayal. The word 'replaced' turns her into a position he deserves to fill, not a person who left for a reason.
'Til you believe that that should be me
He is asking her to accept his framing as fact. Her belief would not change anything, she has already moved on, but he keeps insisting her conviction matters. That is control dressed as vulnerability.
I need to know, should I fight for love or disarm?
This is the only moment where he hesitates. 'Fight' versus 'disarm' suggests he knows persistence might be aggression, but he never actually chooses. The outro answers the question for him.
Never shoulda let you go / I'm never gonna let you go
The shift from past regret to future control happens in two lines. He no longer has the power to prevent what already happened, but the threat underneath the plea finally surfaces. He does not get a vote anymore.
The song ends with a promise that sounds like a threat. Bieber would be surprised to learn that obsessive repetition does not prove devotion, it proves he cannot accept that she left. What started as regret becomes refusal to let her be gone.