The speaker is stuck in an on-again, off-again relationship and knows it. Their partner keeps saying "I love you" and "I won't leave," and the speaker calls these words bullshit, yet admits to believing them every single time. That gap between what the speaker knows and what they do is the heart of the poem.
The feeling is a mix of disgust and helplessness. The speaker finds it "sickening" how easily they get pulled back after a fight, and even admits to craving the pattern of being dropped and then picked up again. There's some self-blame in that, as if the speaker is angry at themselves as much as at the partner.
The last stanza is the bleakest. Even if the partner really did try to change, the speaker expects the night to end the same way: face down in a pillow, crying. The mood is raw and tired, and the short, plain lines make it sound like a confession rather than a performance.