The speaker looks back on a relationship that never quite became what it might have been. Every line takes a big word, like love, mine, hurt, or gone, and tacks "-ish" onto it, so nothing is ever fully claimed. It was love-ish. She was mine-ish. Leaving hurt-ish.
That small suffix is doing a lot of work. It reads like a shield. If the speaker admits the love was real, the loss would be real too, so everything gets softened. The casual, almost joking tone suggests someone trying to shrug it off. But the habit gives him away. People rarely hedge this carefully about things that don't matter to them.
The last line is the most telling. "She is not gone only gone'ish" holds onto a thread of hope, or at least refuses to let go cleanly. The mood is wistful and dry, with a quiet ache under the shrug. The poem seems to say that half-feelings can linger as stubbornly as whole ones.