Alex McLean's "gave you my all" is a short, blunt piece about regret. The speaker looks back on a relationship and asks how anyone could be foolish enough to give everything to a person who barely deserved it. It sounds like a harsh judgment of someone else, but the last two lines turn it around. The speaker admits that the naive person was actually them.
That shift is what gives the poem its weight. The speaker starts out sounding critical, even a little superior, then catches themselves with "But who am I to talk?" The tone softens into honesty, and a bit of embarrassment. There's hurt here, but it's mixed with self-blame rather than anger at the other person.
The mood is quiet, rueful and exposed. The poem doesn't dramatize the pain or explain what happened. It simply admits, in a few plain lines, that loving someone fully can leave you feeling foolish afterward.